diff --git a/src/components/profile/PublishedCssEditor.svelte b/src/components/profile/PublishedCssEditor.svelte
new file mode 100644
index 0000000..70135c6
--- /dev/null
+++ b/src/components/profile/PublishedCssEditor.svelte
@@ -0,0 +1,158 @@
+<script lang="ts">
+  /**
+   * Editor for CSS published through the signed-in account's profile fields.
+   *
+   * This is deliberately separate from Settings' viewer CSS: saving here is a
+   * server mutation and changes what every plspace visitor sees on this profile.
+   */
+  import { useAppServices } from '$lib/app-services'
+  import {
+    profileFieldLimits,
+    publishedCssFieldValues,
+    publishedCssFromFields,
+    replacePublishedCssFields,
+  } from '$lib/stores/theme.svelte'
+
+  const { endpoints, session } = useAppServices()
+
+  let editing = $state(false)
+  let draft = $state('')
+  let busy = $state(false)
+  let error = $state<string | null>(null)
+  let saved = $state(false)
+  let locallyPublishedCss = $state<string | null>(null)
+
+  const limits = $derived(profileFieldLimits(session.instance))
+  const currentCss = $derived(
+    locallyPublishedCss ?? publishedCssFromFields(session.me?.fields),
+  )
+  const chunksNeeded = $derived(publishedCssFieldValues(draft, limits.valueLength).length)
+
+  function decodeFieldValue(value: string): string {
+    const container = document.createElement('div')
+    container.innerHTML = value
+    return container.textContent ?? ''
+  }
+
+  /** Credential-source fields are raw; fall back to decoding rendered fields. */
+  function currentFields(): Array<{ name: string; value: string }> {
+    if (session.me?.source?.fields) {
+      return session.me.source.fields.map(({ name, value }) => ({ name, value }))
+    }
+    return (session.me?.fields ?? []).map(({ name, value }) => ({
+      name,
+      value: decodeFieldValue(value),
+    }))
+  }
+
+  function beginEditing(): void {
+    draft = currentCss
+    error = null
+    saved = false
+    editing = true
+  }
+
+  async function publish(css: string): Promise<void> {
+    if (!session.me || busy) return
+    busy = true
+    error = null
+    saved = false
+    try {
+      const fields = replacePublishedCssFields(currentFields(), css, limits)
+      session.me = await endpoints.updateProfileFields(session.api, fields)
+      locallyPublishedCss = css.trim()
+      draft = locallyPublishedCss
+      editing = false
+      saved = true
+    } catch (cause) {
+      error = cause instanceof Error ? cause.message : 'Could not update your profile CSS.'
+    } finally {
+      busy = false
+    }
+  }
+
+  function remove(): void {
+    if (!confirm('Remove the CSS published on your profile?')) return
+    void publish('')
+  }
+</script>
+
+{#if !session.signedIn || !session.me}
+  <p class="empty-note">
+    <a href="#/login">Sign in</a> to publish CSS on your profile.
+  </p>
+{:else}
+  <div class="published-css-editor">
+    <p class="notice">
+      <strong>Public profile setting:</strong>
+      saving here changes your profile for everyone who views it with plspace—not just this
+      browser. Other clients may display the CSS as ordinary profile fields.
+    </p>
+
+    {#if editing}
+      <label class="field-label" for="published-css">CSS shown on your profile</label>
+      <textarea
+        id="published-css"
+        class="css-editor"
+        bind:value={draft}
+        rows="16"
+        spellcheck="false"
+        aria-describedby="published-css-hint"
+      ></textarea>
+      <p id="published-css-hint" class="field-hint">
+        {draft.length.toLocaleString()} characters.
+        {#if chunksNeeded > 1}
+          plspace will store this in {chunksNeeded} ordered profile fields because
+          {limits.valueLength.toLocaleString()} characters fit in each field on this server.
+        {:else}
+          This fits in one profile field.
+        {/if}
+      </p>
+
+      {#if error}
+        <p class="error-note" role="alert">{error}</p>
+      {/if}
+
+      <div class="field-row">
+        <button
+          type="button"
+          class="button button--primary"
+          disabled={busy || !draft.trim()}
+          onclick={() => void publish(draft)}
+        >
+          {busy ? 'Publishing…' : 'Publish CSS to my profile'}
+        </button>
+        <button type="button" class="button" disabled={busy} onclick={() => (editing = false)}>
+          Cancel
+        </button>
+      </div>
+    {:else}
+      <p>
+        {#if currentCss}
+          Your profile currently publishes
+          <strong>{currentCss.length.toLocaleString()} characters</strong> of CSS.
+        {:else}
+          Your profile does not currently publish any CSS.
+        {/if}
+      </p>
+
+      {#if error}
+        <p class="error-note" role="alert">{error}</p>
+      {:else if saved}
+        <p class="notice" role="status">Your public profile CSS was updated.</p>
+      {/if}
+
+      <div class="field-row">
+        <button type="button" class="button button--primary" onclick={beginEditing}>
+          {currentCss ? 'Edit published CSS' : 'Add CSS to my profile'}
+        </button>
+        {#if currentCss}
+          <button type="button" class="button" disabled={busy} onclick={remove}>
+            Remove published CSS
+          </button>
+        {/if}
+        <a class="button" href={`#/@${session.me.acct}`}>View my profile</a>
+      </div>
+    {/if}
+  </div>
+{/if}
diff --git a/src/components/profile/PublishedCssEditor.test.ts b/src/components/profile/PublishedCssEditor.test.ts
new file mode 100644
index 0000000..0d7a264
--- /dev/null
+++ b/src/components/profile/PublishedCssEditor.test.ts
@@ -0,0 +1,102 @@
+import { fireEvent, render, waitFor } from '@testing-library/svelte'
+import { describe, expect, it, vi } from 'vitest'
+import { APP_SERVICES } from '$lib/app-services'
+import type { CredentialAccount } from '$lib/api/types'
+import { publishedCssFromFields } from '$lib/stores/theme.svelte'
+import { account, session, testServices } from '$test/fixtures'
+import PublishedCssEditor from './PublishedCssEditor.svelte'
+
+function credential(fields: Array<{ name: string; value: string }>): CredentialAccount {
+  return {
+    ...account({ fields }),
+    source: {
+      note: '',
+      fields,
+      privacy: 'public',
+      sensitive: false,
+      language: null,
+    },
+  }
+}
+
+describe('PublishedCssEditor', () => {
+  it('makes the public effect explicit and publishes without losing other fields', async () => {
+    const me = credential([{ name: 'Website', value: 'https://example.test' }])
+    const updateProfileFields = vi.fn(async (_api, fields: Array<{ name: string; value: string }>) =>
+      credential(fields),
+    )
+    const services = testServices({
+      session: session({
+        token: 'token',
+        me,
+        signedIn: true,
+        instance: {
+          title: 'Pleroma',
+          version: '2.9.0',
+          configuration: {
+            accounts: {
+              max_profile_fields: 10,
+              max_profile_field_value_length: 50,
+            },
+          },
+        },
+      }),
+      endpoints: { updateProfileFields },
+    })
+    const view = render(PublishedCssEditor, {
+      context: new Map([[APP_SERVICES, services]]),
+    })
+
+    expect(view.getByText(/everyone who views it with plspace/i)).toBeInTheDocument()
+    await fireEvent.click(view.getByRole('button', { name: 'Add CSS to my profile' }))
+
+    const css = '.one { color: red; }\n.two { color: green; }'
+    await fireEvent.input(view.getByRole('textbox', { name: 'CSS shown on your profile' }), {
+      target: { value: css },
+    })
+    expect(view.getByText(/store this in 2 ordered profile fields/i)).toBeInTheDocument()
+
+    await fireEvent.click(view.getByRole('button', { name: 'Publish CSS to my profile' }))
+    await waitFor(() => expect(updateProfileFields).toHaveBeenCalledOnce())
+
+    const sent = updateProfileFields.mock.calls[0][1]
+    expect(sent[0]).toEqual({ name: 'Website', value: 'https://example.test' })
+    expect(sent.slice(1).map((field) => field.name)).toEqual([
+      'plspace:css1',
+      'plspace:css2',
+    ])
+    expect(publishedCssFromFields(sent.slice(1))).toBe(css)
+    expect(await view.findByText('Your public profile CSS was updated.')).toBeInTheDocument()
+  })
+
+  it('loads and replaces existing CSS chunks', async () => {
+    const me = credential([
+      { name: 'Pronouns', value: 'they/them' },
+      { name: 'plspace:css1', value: '.old {' },
+      { name: 'plspace:css2', value: ' color: red; }' },
+    ])
+    const updateProfileFields = vi.fn(async (_api, fields: Array<{ name: string; value: string }>) =>
+      credential(fields),
+    )
+    const services = testServices({
+      session: session({ token: 'token', me, signedIn: true }),
+      endpoints: { updateProfileFields },
+    })
+    const view = render(PublishedCssEditor, {
+      context: new Map([[APP_SERVICES, services]]),
+    })
+
+    await fireEvent.click(view.getByRole('button', { name: 'Edit published CSS' }))
+    const editor = view.getByRole('textbox', { name: 'CSS shown on your profile' })
+    expect(editor).toHaveValue('.old { color: red; }')
+
+    await fireEvent.input(editor, { target: { value: '.new { color: pink; }' } })
+    await fireEvent.click(view.getByRole('button', { name: 'Publish CSS to my profile' }))
+    await waitFor(() => expect(updateProfileFields).toHaveBeenCalledOnce())
+
+    const sent = updateProfileFields.mock.calls[0][1]
+    expect(sent[0]).toEqual({ name: 'Pronouns', value: 'they/them' })
+    expect(sent.slice(1).map((field) => field.name)).toEqual(['plspace:css1'])
+    expect(publishedCssFromFields(sent.slice(1))).toBe('.new { color: pink; }')
+  })
+})
diff --git a/src/lib/api/endpoints.test.ts b/src/lib/api/endpoints.test.ts
new file mode 100644
index 0000000..f1631e2
--- /dev/null
+++ b/src/lib/api/endpoints.test.ts
@@ -0,0 +1,40 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { ApiClient } from './client'
+import { updateProfileFields } from './endpoints'
+
+afterEach(() => {
+  vi.unstubAllGlobals()
+})
+
+describe('updateProfileFields', () => {
+  it('uses the Pleroma/Mastodon indexed multipart representation', async () => {
+    const fetchMock = vi.fn(async (_url: string, init?: RequestInit) => {
+      expect(init?.method).toBe('PATCH')
+      expect(init?.headers).toBeInstanceOf(Headers)
+      expect((init?.headers as Headers).get('Authorization')).toBe('Bearer token')
+      expect(init?.body).toBeInstanceOf(FormData)
+      const form = init?.body as FormData
+      expect([...form.entries()]).toEqual([
+        ['fields_attributes[0][name]', 'Website'],
+        ['fields_attributes[0][value]', 'https://example.test'],
+        ['fields_attributes[1][name]', 'plspace:css1'],
+        ['fields_attributes[1][value]', 'body { color: pink; }'],
+      ])
+      return new Response(JSON.stringify({ id: 'account-1', fields: [] }), {
+        status: 200,
+        headers: { 'Content-Type': 'application/json' },
+      })
+    })
+    vi.stubGlobal('fetch', fetchMock)
+
+    await updateProfileFields(new ApiClient('example.test', 'token'), [
+      { name: 'Website', value: 'https://example.test' },
+      { name: 'plspace:css1', value: 'body { color: pink; }' },
+    ])
+
+    expect(fetchMock).toHaveBeenCalledWith(
+      'https://example.test/api/v1/accounts/update_credentials',
+      expect.any(Object),
+    )
+  })
+})
diff --git a/src/lib/api/endpoints.ts b/src/lib/api/endpoints.ts
index 27d7263..570d01c 100644
--- a/src/lib/api/endpoints.ts
+++ b/src/lib/api/endpoints.ts
@@ -85,6 +85,27 @@ export function verifyCredentials(api: ApiClient): Promise<CredentialAccount> {
   return api.get<CredentialAccount>('/api/v1/accounts/verify_credentials')
 }
 
+/**
+ * Replace the signed-in account's profile fields while leaving every other
+ * credential untouched. Mastodon and Pleroma both accept this indexed
+ * multipart shape; Pleroma-FE uses the same representation.
+ */
+export async function updateProfileFields(
+  api: ApiClient,
+  fields: Array<{ name: string; value: string }>,
+): Promise<CredentialAccount> {
+  const form = new FormData()
+  fields.forEach((field, index) => {
+    form.append(`fields_attributes[${index}][name]`, field.name)
+    form.append(`fields_attributes[${index}][value]`, field.value)
+  })
+  const { data } = await api.raw<CredentialAccount>('/api/v1/accounts/update_credentials', {
+    method: 'PATCH',
+    form,
+  })
+  return data
+}
+
 export function fetchAccount(api: ApiClient, id: string): Promise<Account> {
   return api.get<Account>(`/api/v1/accounts/${encodeURIComponent(id)}`)
 }
diff --git a/src/lib/api/types.ts b/src/lib/api/types.ts
index 6764553..39f2893 100644
--- a/src/lib/api/types.ts
+++ b/src/lib/api/types.ts
@@ -266,11 +266,30 @@ export interface InstanceInfo {
       max_characters?: number
       max_media_attachments?: number
     }
+    accounts?: {
+      max_profile_fields?: number
+      /** Pleroma v2 names. */
+      profile_field_name_limit?: number
+      profile_field_value_limit?: number
+      /** Mastodon-compatible aliases used by some implementations. */
+      max_profile_field_name_length?: number
+      max_profile_field_value_length?: number
+    }
   }
   registrations?: boolean | { enabled?: boolean }
   contact_account?: Account | null
-  /** Pleroma reports its "real" upstream here. */
-  pleroma?: unknown
+  /** Pleroma reports its "real" upstream and field limits here. */
+  pleroma?: {
+    metadata?: {
+      fields_limits?: {
+        max_fields?: number
+        name_length?: number
+        value_length?: number
+      }
+      [key: string]: unknown
+    }
+    [key: string]: unknown
+  }
 }
 
 export interface SearchResults {
diff --git a/src/lib/stores/theme.svelte.ts b/src/lib/stores/theme.svelte.ts
index 5a3d507..ebf68ce 100644
--- a/src/lib/stores/theme.svelte.ts
+++ b/src/lib/stores/theme.svelte.ts
@@ -16,6 +16,8 @@
  * run script.
  */
 
+import type { InstanceInfo } from '../api/types'
+
 const VIEWER_STYLE_ID = 'user-stylesheet'
 const PROFILE_STYLE_ID = 'profile-stylesheet'
 const STORAGE_KEY = 'plspace:viewer-css'
@@ -26,6 +28,228 @@ export const PROFILE_SCOPE = '.profile-page'
 /** Field names checked, in order, for a profile's published stylesheet. */
 export const CSS_FIELD_NAMES = ['css', 'style', 'layout', 'stylesheet']
 
+const NAMESPACED_CSS_FIELD_PATTERN = /^plspace:css(\d+)$/i
+const LEGACY_CSS_FIELD_PATTERN = /^(css|style|layout|stylesheet)(?:[\s_-]+(\d+))?$/i
+const ENCODED_CSS_PREFIX = 'plspace-css-b64:'
+
+export interface ProfileFieldLimits {
+  maxFields: number
+  nameLength: number
+  valueLength: number
+}
+
+/** Normalize Mastodon v2 and Pleroma extension shapes, with safe old-server defaults. */
+export function profileFieldLimits(instance: InstanceInfo | null): ProfileFieldLimits {
+  const accounts = instance?.configuration?.accounts
+  const pleroma = instance?.pleroma?.metadata?.fields_limits
+  const isPleroma = Boolean(instance?.pleroma)
+  return {
+    maxFields: accounts?.max_profile_fields ?? pleroma?.max_fields ?? (isPleroma ? 10 : 4),
+    nameLength:
+      accounts?.profile_field_name_limit ??
+      accounts?.max_profile_field_name_length ??
+      pleroma?.name_length ??
+      255,
+    valueLength:
+      accounts?.profile_field_value_limit ??
+      accounts?.max_profile_field_value_length ??
+      pleroma?.value_length ??
+      (isPleroma ? 2048 : 255),
+  }
+}
+
+function fieldText(field: { value: string }): string {
+  const container = document.createElement('div')
+  container.innerHTML = field.value
+  for (const br of Array.from(container.querySelectorAll('br'))) {
+    br.replaceWith(document.createTextNode('\n'))
+  }
+  for (const block of Array.from(container.querySelectorAll('p, div, li'))) {
+    if (block.nextSibling) block.append(document.createTextNode('\n'))
+  }
+  return container.textContent ?? ''
+}
+
+function cssField(
+  field: { name: string },
+): { namespace: 'plspace' | 'legacy'; base: string; part: number } | null {
+  const name = field.name.trim()
+  const namespaced = NAMESPACED_CSS_FIELD_PATTERN.exec(name)
+  if (namespaced) {
+    return { namespace: 'plspace', base: 'css', part: Number(namespaced[1]) }
+  }
+  const legacy = LEGACY_CSS_FIELD_PATTERN.exec(name)
+  if (!legacy) return null
+  return {
+    namespace: 'legacy',
+    base: legacy[1].toLowerCase(),
+    part: legacy[2] ? Number(legacy[2]) : 1,
+  }
+}
+
+/** Reassemble a single CSS field or the ordered chunks written by plspace. */
+export function publishedCssFromFields(
+  fields: Array<{ name: string; value: string }> | undefined,
+): string {
+  if (!fields?.length) return ''
+  const namespaced = fields
+    .map((field, index) => ({ field, index, parsed: cssField(field) }))
+    .filter((entry) => entry.parsed?.namespace === 'plspace')
+    .sort((a, b) => (a.parsed!.part - b.parsed!.part) || (a.index - b.index))
+  if (namespaced.length > 0) {
+    const values = namespaced.map(({ field }) => fieldText(field))
+    if (values.every((value) => value.startsWith(ENCODED_CSS_PREFIX))) {
+      try {
+        return decodeCss(
+          values.map((value) => value.slice(ENCODED_CSS_PREFIX.length)).join(''),
+        ).trim()
+      } catch {
+        // Keep profiles readable if a field was edited or truncated elsewhere.
+        return ''
+      }
+    }
+    return values.join('').trim()
+  }
+
+  for (const preferred of CSS_FIELD_NAMES) {
+    const chunks = fields
+      .map((field, index) => ({ field, index, parsed: cssField(field) }))
+      .filter(
+        (entry) =>
+          entry.parsed?.namespace === 'legacy' && entry.parsed.base === preferred,
+      )
+      .sort((a, b) => (a.parsed!.part - b.parsed!.part) || (a.index - b.index))
+    if (chunks.length > 0) return chunks.map(({ field }) => fieldText(field)).join('').trim()
+  }
+  return ''
+}
+
+/**
+ * Browsers normalize bare LF line endings to CRLF when serializing FormData,
+ * and Pleroma validates the decoded multipart value. Budget two characters for
+ * each newline so a nominal 2,048-character chunk cannot arrive over the limit.
+ *
+ * Split on rule boundaries when possible while otherwise retaining the source.
+ * Chunks are concatenated without a separator, including when a very long
+ * quoted data URI has to be split in its middle.
+ */
+export function splitPublishedCss(css: string, limit: number): string[] {
+  const source = css.replace(/\r\n?/g, '\n').trim()
+  if (!source) return []
+  const safeLimit = Math.max(1, Math.floor(limit))
+  const chunks: string[] = []
+  let rest = source
+
+  while (multipartFieldLength(rest) > safeLimit) {
+    let windowEnd = 0
+    let encodedLength = 0
+    while (windowEnd < rest.length) {
+      const width = rest[windowEnd] === '\n' ? 2 : 1
+      if (encodedLength + width > safeLimit) break
+      encodedLength += width
+      windowEnd += 1
+    }
+    // A one-character limit can still make progress on a newline.
+    if (windowEnd === 0) windowEnd = 1
+
+    const window = rest.slice(0, windowEnd)
+    let cut = window.lastIndexOf('}')
+    if (cut >= 0) cut += 1
+    else {
+      cut = window.lastIndexOf('\n')
+      if (cut <= 0) cut = windowEnd
+    }
+    chunks.push(rest.slice(0, cut))
+    rest = rest.slice(cut)
+  }
+  if (rest) chunks.push(rest)
+  return chunks
+}
+
+/** Length after the newline normalization used for multipart form fields. */
+export function multipartFieldLength(value: string): number {
+  let length = value.length
+  for (let index = 0; index < value.length; index += 1) {
+    if (value[index] === '\n' && value[index - 1] !== '\r') length += 1
+  }
+  return length
+}
+
+function encodeCss(value: string): string {
+  const bytes = new TextEncoder().encode(value)
+  let binary = ''
+  const windowSize = 0x8000
+  for (let index = 0; index < bytes.length; index += windowSize) {
+    binary += String.fromCharCode(...bytes.subarray(index, index + windowSize))
+  }
+  return btoa(binary).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '')
+}
+
+function decodeCss(value: string): string {
+  const base64 = value.replace(/-/g, '+').replace(/_/g, '/')
+  const padded = base64.padEnd(Math.ceil(base64.length / 4) * 4, '=')
+  const binary = atob(padded)
+  const bytes = Uint8Array.from(binary, (character) => character.charCodeAt(0))
+  return new TextDecoder().decode(bytes)
+}
+
+/**
+ * Encode published CSS before placing it in profile fields.
+ *
+ * Pleroma linkifies raw profile-field values before enforcing its configured
+ * value limit. CSS commonly contains URLs and hashtag-shaped tokens such as
+ * `#fff`, so a raw value under the advertised limit can expand into HTML over
+ * that limit. Base64url has no linkifiable syntax, making its server-side
+ * length identical to the length measured here.
+ */
+export function publishedCssFieldValues(css: string, limit: number): string[] {
+  const source = css.replace(/\r\n?/g, '\n').trim()
+  if (!source) return []
+
+  const capacity = Math.floor(limit) - ENCODED_CSS_PREFIX.length
+  if (capacity < 1) {
+    throw new Error('This server’s profile field-value limit is too small for encoded CSS.')
+  }
+
+  const encoded = encodeCss(source)
+  const values: string[] = []
+  for (let index = 0; index < encoded.length; index += capacity) {
+    values.push(ENCODED_CSS_PREFIX + encoded.slice(index, index + capacity))
+  }
+  return values
+}
+
+/**
+ * Preserve normal profile fields and replace all prior CSS chunks atomically.
+ * Legacy CSS fields are migrated to the unambiguous `plspace:css1` namespace.
+ */
+export function replacePublishedCssFields(
+  fields: Array<{ name: string; value: string }>,
+  css: string,
+  limits: ProfileFieldLimits,
+): Array<{ name: string; value: string }> {
+  const existingCss = fields.map((field) => ({ field, parsed: cssField(field) }))
+  const ordinary = existingCss
+    .filter((entry) => !entry.parsed)
+    .map(({ field }) => ({ name: field.name, value: field.value }))
+  const chunks = publishedCssFieldValues(css, limits.valueLength)
+  const cssFields = chunks.map((value, index) => ({
+    name: `plspace:css${index + 1}`,
+    value,
+  }))
+
+  if (ordinary.length + cssFields.length > limits.maxFields) {
+    const available = Math.max(0, limits.maxFields - ordinary.length)
+    throw new Error(
+      `This server has room for ${available} CSS field${available === 1 ? '' : 's'}, but this stylesheet needs ${cssFields.length}. Shorten it or remove another profile field.`,
+    )
+  }
+  if (cssFields.some((field) => field.name.length > limits.nameLength)) {
+    throw new Error('This server’s profile field-name limit is too small for chunked CSS.')
+  }
+  return [...ordinary, ...cssFields]
+}
+
 /**
  * Get (or create) a style element, always moving it to the end of `<head>`.
  *
@@ -194,14 +418,6 @@ export const theme = new Theme()
 export function profileCssFromFields(
   fields: Array<{ name: string; value: string }> | undefined,
 ): string | null {
-  if (!fields?.length) return null
-  for (const field of fields) {
-    if (!CSS_FIELD_NAMES.includes(field.name.trim().toLowerCase())) continue
-    // Field values arrive as HTML; take the text and undo entity escaping.
-    const container = document.createElement('div')
-    container.innerHTML = field.value
-    const text = (container.textContent ?? '').trim()
-    if (text.includes('{')) return text
-  }
-  return null
+  const css = publishedCssFromFields(fields)
+  return css.includes('{') ? css : null
 }
diff --git a/src/lib/stores/theme.test.ts b/src/lib/stores/theme.test.ts
new file mode 100644
index 0000000..1e49539
--- /dev/null
+++ b/src/lib/stores/theme.test.ts
@@ -0,0 +1,144 @@
+import { describe, expect, it } from 'vitest'
+import {
+  profileCssFromFields,
+  profileFieldLimits,
+  multipartFieldLength,
+  publishedCssFieldValues,
+  publishedCssFromFields,
+  replacePublishedCssFields,
+  splitPublishedCss,
+} from './theme.svelte'
+
+describe('published profile CSS fields', () => {
+  it('reads ordinary and chunked CSS fields in numeric order', () => {
+    const fields = [
+      { name: 'Website', value: '<a href="https://example.test">example</a>' },
+      { name: 'plspace:css3', value: '<p>.three { color: blue; }</p>' },
+      { name: 'plspace:css1', value: '<p>.one { color: red; }</p>' },
+      { name: 'plspace:css2', value: '<p>.two { color: green; }</p>' },
+    ]
+
+    expect(publishedCssFromFields(fields)).toBe(
+      '.one { color: red; }.two { color: green; }.three { color: blue; }',
+    )
+    expect(profileCssFromFields(fields)).toContain('.three { color: blue; }')
+  })
+
+  it('splits long stylesheets on complete rule boundaries', () => {
+    const css = '.one { color: red; }\n.two { color: green; }\n.three { color: blue; }'
+    const chunks = splitPublishedCss(css, 42)
+    expect(chunks.length).toBeGreaterThan(1)
+    expect(chunks.every((chunk) => multipartFieldLength(chunk) <= 42)).toBe(true)
+    expect(chunks.join('')).toBe(css)
+  })
+
+  it('budgets for FormData expanding line feeds to CRLF', () => {
+    const css = Array.from({ length: 20 }, (_, index) => `.r${index} {\n  color: pink;\n}`).join(
+      '\n',
+    )
+    const chunks = splitPublishedCss(css, 80)
+
+    expect(chunks.length).toBeGreaterThan(1)
+    expect(chunks.every((chunk) => multipartFieldLength(chunk) <= 80)).toBe(true)
+    expect(chunks.join('')).toBe(css)
+  })
+
+  it('stores CSS as non-linkifiable chunks and decodes Unicode exactly', () => {
+    const css =
+      '.profile { color: #fff; background: url("https://example.test/image.png"); }\n/* 日本語 🌸 */'
+    const values = publishedCssFieldValues(css, 48)
+
+    expect(values.length).toBeGreaterThan(1)
+    expect(values.every((value) => value.length <= 48)).toBe(true)
+    expect(values.every((value) => /^plspace-css-b64:[A-Za-z0-9_-]+$/.test(value))).toBe(true)
+    expect(
+      publishedCssFromFields(
+        values.map((value, index) => ({ name: `plspace:css${index + 1}`, value })),
+      ),
+    ).toBe(css)
+  })
+
+  it('replaces old CSS chunks while preserving unrelated profile fields', () => {
+    const result = replacePublishedCssFields(
+      [
+        { name: 'Website', value: 'https://example.test' },
+        { name: 'style', value: 'old' },
+        { name: 'style 2', value: 'old continuation' },
+        { name: 'Pronouns', value: 'they/them' },
+      ],
+      '.one { color: red; }\n.two { color: green; }',
+      { maxFields: 6, nameLength: 255, valueLength: 55 },
+    )
+
+    expect(result.slice(0, 2)).toEqual([
+      { name: 'Website', value: 'https://example.test' },
+      { name: 'Pronouns', value: 'they/them' },
+    ])
+    expect(result.slice(2).map((field) => field.name)).toEqual([
+      'plspace:css1',
+      'plspace:css2',
+    ])
+    expect(publishedCssFromFields(result.slice(2))).toBe(
+      '.one { color: red; }\n.two { color: green; }',
+    )
+  })
+
+  it('removes only CSS fields when publishing an empty value', () => {
+    expect(
+      replacePublishedCssFields(
+        [
+          { name: 'css', value: 'body {}' },
+          { name: 'plspace:css2', value: '.more {}' },
+          { name: 'Location', value: 'Tokyo' },
+        ],
+        '',
+        { maxFields: 4, nameLength: 255, valueLength: 255 },
+      ),
+    ).toEqual([{ name: 'Location', value: 'Tokyo' }])
+  })
+
+  it('rejects a stylesheet that exceeds the server field count', () => {
+    expect(() =>
+      replacePublishedCssFields(
+        [{ name: 'Website', value: 'https://example.test' }],
+        '.a{color:red}.b{color:blue}.c{color:green}',
+        { maxFields: 2, nameLength: 255, valueLength: 30 },
+      ),
+    ).toThrow(/room for 1 CSS field/)
+  })
+
+  it('normalizes both Mastodon and Pleroma field-limit shapes', () => {
+    expect(
+      profileFieldLimits({
+        title: 'Mastodon',
+        version: '4.5.0',
+        configuration: {
+          accounts: {
+            max_profile_fields: 4,
+            max_profile_field_name_length: 255,
+            max_profile_field_value_length: 500,
+          },
+        },
+      }),
+    ).toEqual({ maxFields: 4, nameLength: 255, valueLength: 500 })
+
+    expect(
+      profileFieldLimits({
+        title: 'Pleroma',
+        version: '2.9.0',
+        configuration: {
+          accounts: {
+            max_profile_fields: 10,
+            profile_field_name_limit: 512,
+            profile_field_value_limit: 2048,
+          },
+        },
+        pleroma: {
+          metadata: {
+            fields_limits: { max_fields: 9, name_length: 500, value_length: 2000 },
+          },
+        },
+      }),
+    ).toEqual({ maxFields: 10, nameLength: 512, valueLength: 2048 })
+  })
+})
diff --git a/src/lib/util/profile.test.ts b/src/lib/util/profile.test.ts
new file mode 100644
index 0000000..17f2410
--- /dev/null
+++ b/src/lib/util/profile.test.ts
@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest'
+import { account } from '$test/fixtures'
+import { buildProfileView } from './profile'
+
+describe('buildProfileView', () => {
+  it('hides namespaced plspace storage fields from visible profile details', () => {
+    const profile = buildProfileView(
+      account({
+        fields: [
+          { name: 'Website', value: '<a href="https://example.test">example.test</a>' },
+          { name: 'plspace:css1', value: 'plspace-css-b64:YWJj' },
+          { name: ' PLSPACE:future-setting ', value: 'internal' },
+        ],
+      }),
+    )
+
+    expect(profile.details).toHaveLength(1)
+    expect(profile.details[0].name).toBe('Website')
+    expect(profile.details[0].value).toContain('example.test')
+  })
+})
diff --git a/src/lib/util/profile.ts b/src/lib/util/profile.ts
index dbf5f0e..d155870 100644
--- a/src/lib/util/profile.ts
+++ b/src/lib/util/profile.ts
@@ -132,6 +132,10 @@ export function buildProfileView(account: Account): ProfileView {
 
   for (const field of account.fields ?? []) {
     const key = field.name.trim().toLowerCase()
+    // `plspace:` fields are application storage, not user-facing profile
+    // details. Keep them on the Account for features such as published CSS,
+    // but never turn them into visible name/value rows.
+    if (key.startsWith('plspace:')) continue
     if (CHROME_FIELDS.has(key)) continue
 
     const value = renderHtml(field.value, { emojis: account.emojis })
diff --git a/src/routes/Settings.svelte b/src/routes/Settings.svelte
index d9d41dc..385dd1a 100644
--- a/src/routes/Settings.svelte
+++ b/src/routes/Settings.svelte
@@ -13,6 +13,7 @@
   import { instanceDomain } from '$lib/api/endpoints'
   import { displayNameOf, profilePath } from '$lib/util/profile'
   import Module from '$components/common/Module.svelte'
+  import PublishedCssEditor from '$components/profile/PublishedCssEditor.svelte'
 
   const { session, theme } = useAppServices()
 
@@ -130,11 +131,15 @@
       </ul>
     </Module>
 
-    <Module title="Your CSS" variant="band">
+    <Module title="CSS for this browser only" variant="band">
+      <p class="notice">
+        <strong>Private viewing setting:</strong>
+        this changes how plspace looks only for you, in this browser. It does not update your
+        profile, and nobody else can see it.
+      </p>
       <p>
-        This is applied to every page you view in plspace. Overriding the custom properties in
-        <code>styles/tokens.css</code> retints the entire app; the class hooks below let you go
-        further.
+        Overriding the custom properties in <code>styles/tokens.css</code> retints the entire app;
+        the class hooks below let you go further.
       </p>
 
       <label class="visually-hidden" for="viewer-css">Your CSS</label>
@@ -174,32 +179,22 @@
         </span>
       </label>
       <p class="field-hint">
-        A profile can publish a stylesheet by putting CSS in a profile field named
-        {#each CSS_FIELD_NAMES as name, index (name)}<code>{name}</code>{#if index < CSS_FIELD_NAMES.length - 1}, {/if}{/each}.
+        plspace publishes layouts in ordered fields named <code>plspace:css1</code>,
+        <code>plspace:css2</code>, and so on. Legacy
+        {#each CSS_FIELD_NAMES as name, index (name)}<code>{name}</code>{#if index < CSS_FIELD_NAMES.length - 1}, {/if}{/each}
+        fields are still understood.
         Their rules are rewritten to apply only inside <code>{PROFILE_SCOPE}</code>, so a profile
         can restyle its own page but not the rest of plspace.
       </p>
     </Module>
 
-    <Module title="Publish your own layout" variant="band">
+    <Module title="CSS published on your profile" variant="band">
       <p>
-        Add a profile field on <strong>{domain || 'your server'}</strong> named <code>css</code> and
-        paste a stylesheet into its value. Anyone viewing your profile in plspace sees it. Since
-        it's an ordinary profile field, it survives elsewhere too &mdash; other clients just show it
-        as text.
+        This editor writes the layout into profile fields on
+        <strong>{domain || 'your server'}</strong>. Anyone who visits your profile with plspace
+        will receive it automatically.
       </p>
-      {#if session.signedIn}
-        <p>
-          <a
-            class="button"
-            href={`https://${session.host}/settings/profile`}
-            target="_blank"
-            rel="noopener noreferrer"
-          >
-            Edit your profile on {domain}
-          </a>
-        </p>
-      {/if}
+      <PublishedCssEditor />
     </Module>
 
     <Module title="Class reference" variant="band">
diff --git a/src/routes/Settings.test.ts b/src/routes/Settings.test.ts
new file mode 100644
index 0000000..b735e51
--- /dev/null
+++ b/src/routes/Settings.test.ts
@@ -0,0 +1,22 @@
+import { render } from '@testing-library/svelte'
+import { describe, expect, it } from 'vitest'
+import { APP_SERVICES } from '$lib/app-services'
+import { testServices } from '$test/fixtures'
+import Settings from './Settings.svelte'
+
+describe('Settings CSS language', () => {
+  it('distinguishes private viewer CSS from publicly published profile CSS', () => {
+    const view = render(Settings, {
+      context: new Map([[APP_SERVICES, testServices()]]),
+    })
+
+    expect(
+      view.getByRole('heading', { name: 'CSS for this browser only' }),
+    ).toBeInTheDocument()
+    expect(view.getByText(/nobody else can see it/i)).toBeInTheDocument()
+    expect(
+      view.getByRole('heading', { name: 'CSS published on your profile' }),
+    ).toBeInTheDocument()
+    expect(view.getByText(/anyone who visits your profile with plspace/i)).toBeInTheDocument()
+  })
+})