diff --git a/internal/api/themes.go b/internal/api/themes.go
index cd36b47..0325e4b 100644
--- a/internal/api/themes.go
+++ b/internal/api/themes.go
@@ -1,6 +1,7 @@
 package api
 
 import (
+	_ "embed"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -19,6 +20,29 @@ type themeManifest struct {
 	Version string `json:"version"`
 }
 
+//go:embed themes/white.css
+var whiteThemeCSS string
+
+//go:embed themes/black.css
+var blackThemeCSS string
+
+var builtinThemes = []struct {
+	themeManifest
+	css string
+}{
+	{themeManifest{"white", "白色", "1"}, whiteThemeCSS},
+	{themeManifest{"black", "黑色", "1"}, blackThemeCSS},
+}
+
+func builtinTheme(id string) (themeManifest, string, bool) {
+	for _, theme := range builtinThemes {
+		if theme.ID == id {
+			return theme.themeManifest, theme.css, true
+		}
+	}
+	return themeManifest{}, "", false
+}
+
 func readThemeFile(root *os.Root, name string, limit int64) ([]byte, error) {
 	f, err := root.Open(name)
 	if err != nil {
@@ -43,6 +67,9 @@ func readThemeFile(root *os.Root, name string, limit int64) ([]byte, error) {
 }
 
 func (s *Server) readTheme(id string) (themeManifest, string, error) {
+	if manifest, css, ok := builtinTheme(id); ok {
+		return manifest, css, nil
+	}
 	var manifest themeManifest
 	if !themeIDPattern.MatchString(id) || id == "default" || s.ThemesDir == "" {
 		return manifest, "", fs.ErrNotExist
@@ -73,6 +100,9 @@ func (s *Server) readTheme(id string) (themeManifest, string, error) {
 
 func (s *Server) listThemes(w http.ResponseWriter, r *http.Request) {
 	themes := []themeManifest{{ID: "default", Name: "默认", Version: "1"}}
+	for _, theme := range builtinThemes {
+		themes = append(themes, theme.themeManifest)
+	}
 	if s.ThemesDir != "" {
 		entries, err := os.ReadDir(s.ThemesDir)
 		if err != nil && !errors.Is(err, fs.ErrNotExist) {
@@ -80,6 +110,9 @@ func (s *Server) listThemes(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		for _, entry := range entries {
+			if _, _, ok := builtinTheme(entry.Name()); ok {
+				continue
+			}
 			if !entry.IsDir() || !themeIDPattern.MatchString(entry.Name()) || entry.Name() == "default" {
 				continue
 			}
diff --git a/internal/api/themes/black.css b/internal/api/themes/black.css
new file mode 100644
index 0000000..4936f54
--- /dev/null
+++ b/internal/api/themes/black.css
@@ -0,0 +1,30 @@
+:root {
+  color-scheme: dark;
+  --rm-bg: #0b0b0c;
+  --rm-sidebar-bg: #111113;
+  --rm-text: #e6e8eb;
+  --rm-text-muted: #9b9fa8;
+  --rm-divider: #2b2d33;
+  --rm-accent: #8eafff;
+  --rm-accent-strong: #b3c9ff;
+  --rm-selection: rgba(142, 175, 255, 0.25);
+  --rm-hover: rgba(230, 232, 235, 0.065);
+  --rm-active: rgba(142, 175, 255, 0.14);
+  --rm-danger: #ff8291;
+  --rm-warn-bg: #2c2413;
+  --rm-warn-text: #e8c477;
+  --rm-shadow: 0 12px 36px rgba(0, 0, 0, 0.6);
+  --rm-inline-code-bg: #202127;
+  --rm-inline-code-text: #c3d5f5;
+  --rm-code-bg: #18191e;
+  --rm-code-text: #e1e4e8;
+  --rm-highlight-bg: rgba(232, 196, 119, 0.25);
+}
+
+/* 浅蓝按钮使用深色文字，保持选中状态与操作按钮的对比度。 */
+.rm-btn-primary,
+.rm-btn-primary:hover,
+.rm-segmented button.on,
+.rm-share-password button {
+  color: #0b0b0c;
+}
diff --git a/internal/api/themes/white.css b/internal/api/themes/white.css
new file mode 100644
index 0000000..764d712
--- /dev/null
+++ b/internal/api/themes/white.css
@@ -0,0 +1,22 @@
+:root {
+  color-scheme: light;
+  --rm-bg: #ffffff;
+  --rm-sidebar-bg: #f6f7f9;
+  --rm-text: #202124;
+  --rm-text-muted: #656b75;
+  --rm-divider: #e3e6eb;
+  --rm-accent: #2563eb;
+  --rm-accent-strong: #1d4ed8;
+  --rm-selection: rgba(37, 99, 235, 0.18);
+  --rm-hover: rgba(32, 33, 36, 0.045);
+  --rm-active: rgba(37, 99, 235, 0.10);
+  --rm-danger: #c42b3a;
+  --rm-warn-bg: #fff8e6;
+  --rm-warn-text: #855600;
+  --rm-shadow: 0 12px 36px rgba(24, 31, 44, 0.12);
+  --rm-inline-code-bg: #f0f2f5;
+  --rm-inline-code-text: #40536d;
+  --rm-code-bg: #292d3e;
+  --rm-code-text: #e1e4e8;
+  --rm-highlight-bg: #fff0a8;
+}
diff --git a/internal/api/themes_test.go b/internal/api/themes_test.go
index 4851d0c..d06d60c 100644
--- a/internal/api/themes_test.go
+++ b/internal/api/themes_test.go
@@ -29,9 +29,15 @@ func TestThemeAndShareAppearanceBoundaries(t *testing.T) {
 		t.Fatalf("匿名用户不应读取主题，得到 %d", code)
 	}
 	themes := decode[struct{ Themes []themeManifest }](t, f.do(f.admin, "GET", "/api/v1/themes", "", nil))
-	if len(themes.Themes) != 2 || themes.Themes[1].ID != "paper" {
+	if len(themes.Themes) != 4 || themes.Themes[0].ID != "default" || themes.Themes[1].ID != "white" || themes.Themes[2].ID != "black" || themes.Themes[3].ID != "paper" {
 		t.Fatalf("主题列表错误：%+v", themes.Themes)
 	}
+	for _, id := range []string{"white", "black"} {
+		theme := decode[map[string]string](t, f.do(f.admin, "GET", "/api/v1/themes/"+id, "", nil))
+		if theme["id"] != id || !strings.Contains(theme["css"], "--rm-bg:") {
+			t.Fatalf("内置主题未提供配色：%s", id)
+		}
+	}
 	theme := decode[map[string]string](t, f.do(f.admin, "GET", "/api/v1/themes/paper", "", nil))
 	if !strings.Contains(theme["css"], "#faf6ed") {
 		t.Fatal("未读取到主题 CSS")
diff --git a/web/src/app/AppearanceSettings.vue b/web/src/app/AppearanceSettings.vue
index 2babe22..26af0a7 100644
--- a/web/src/app/AppearanceSettings.vue
+++ b/web/src/app/AppearanceSettings.vue
@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import { computed, onMounted, ref } from 'vue'
 import { api, ApiError, type Theme } from './api'
-import { appearancePaused, type CssSnippet } from '../themes/appearance'
+import { appearancePaused, fixedThemeMode, type CssSnippet } from '../themes/appearance'
 import { loadSettings, reloadTheme, settings, updateSettings, type Settings } from './settings'
 import { toast } from './workspace'
 
@@ -11,6 +11,7 @@ const busy = ref(false)
 const editing = ref<string | null>(null)
 const draft = ref({ name: '', css: '' })
 const missingTheme = computed(() => !themes.value.some((theme) => theme.id === settings.theme))
+const fixedMode = computed(() => fixedThemeMode(settings.theme))
 
 async function refreshThemes() {
   error.value = ''
@@ -74,7 +75,7 @@ async function reset() {
   <p v-if="appearancePaused" class="rm-appearance-note">已临时停用主题和 CSS。可恢复默认外观后重新打开页面。</p>
   <div class="rm-setting">
     <label for="rm-color-mode" class="rm-setting-label">明暗模式</label>
-    <select id="rm-color-mode" :value="settings.colorMode" :disabled="busy" @change="change({ colorMode: ($event.target as HTMLSelectElement).value as Settings['colorMode'] })">
+    <select id="rm-color-mode" :value="fixedMode ?? settings.colorMode" :disabled="busy || !!fixedMode" @change="change({ colorMode: ($event.target as HTMLSelectElement).value as Settings['colorMode'] })">
       <option value="system">跟随系统</option><option value="light">浅色</option><option value="dark">深色</option>
     </select>
   </div>
@@ -87,7 +88,8 @@ async function reset() {
     <button class="rm-btn" :disabled="busy" @click="refreshThemes">刷新列表</button>
   </div>
   <p v-if="error" class="rm-appearance-note rm-auth-error">{{ error }}</p>
-  <p class="rm-appearance-note">主题从服务器数据目录的 themes 文件夹读取；主题和已启用的 CSS 也会应用到分享页。</p>
+  <p v-if="fixedMode" class="rm-appearance-note">白色、黑色主题固定使用对应明暗模式；切换回默认或自定义主题后使用原来的明暗设置。</p>
+  <p class="rm-appearance-note">可选择内置主题，或从服务器数据目录的 themes 文件夹添加主题；主题和已启用的 CSS 也会应用到分享页。</p>
   <div class="rm-setting"><span class="rm-setting-label">CSS 片段</span><button class="rm-btn" :disabled="busy" @click="edit()">新建片段</button></div>
   <div v-for="snippet in settings.cssSnippets" :key="snippet.id" class="rm-snippet-row">
     <label><input type="checkbox" :checked="snippet.enabled" :disabled="busy" @change="toggle(snippet)" />{{ snippet.name }}</label>
diff --git a/web/src/themes/appearance.ts b/web/src/themes/appearance.ts
index 199711c..11069b9 100644
--- a/web/src/themes/appearance.ts
+++ b/web/src/themes/appearance.ts
@@ -13,6 +13,11 @@ export interface Appearance {
 
 export const appearancePaused = new URLSearchParams(location.search).has('reset-appearance')
 
+export function fixedThemeMode(theme: string): 'light' | 'dark' | undefined {
+  if (theme === 'white') return 'light'
+  if (theme === 'black') return 'dark'
+}
+
 export function sanitizeAppearance(raw: Record<string, unknown>): Appearance {
   return {
     colorMode: raw.colorMode === 'light' || raw.colorMode === 'dark' ? raw.colorMode : 'system',
@@ -40,7 +45,7 @@ function style(id: string, css: string) {
 }
 
 function render() {
-  const mode = appearancePaused ? 'system' : current.colorMode
+  const mode = appearancePaused ? 'system' : fixedThemeMode(current.theme) ?? current.colorMode
   const dark = mode === 'system' ? darkMode.matches : mode === 'dark'
   const signature = JSON.stringify([dark, appearancePaused ? '' : [current.theme, themeCSS, current.cssSnippets]])
   if (signature === rendered) return