diff --git a/apps/readest-app/public/locales/de/translation.json b/apps/readest-app/public/locales/de/translation.json
index 48018527..7f4e91b9 100644
--- a/apps/readest-app/public/locales/de/translation.json
+++ b/apps/readest-app/public/locales/de/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Über Readest",
   "Add your notes here...": "Fügen Sie hier Ihre Notizen hinzu...",
   "Animation": "Animation",
+  "Apply": "Anwenden",
   "Are you sure to delete the selected books?": "Möchten Sie die ausgewählten Bücher wirklich löschen?",
   "Auto Mode": "Automatischer Modus",
   "Behavior": "Verhalten",
diff --git a/apps/readest-app/public/locales/es/translation.json b/apps/readest-app/public/locales/es/translation.json
index 7f36ead2..f1c4fa5f 100644
--- a/apps/readest-app/public/locales/es/translation.json
+++ b/apps/readest-app/public/locales/es/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Acerca de Readest",
   "Add your notes here...": "Añade tus notas aquí...",
   "Animation": "Animación",
+  "Apply": "Aplicar",
   "Are you sure to delete the selected books?": "¿Estás seguro de eliminar los libros seleccionados?",
   "Auto Mode": "Modo automático",
   "Behavior": "Comportamiento",
diff --git a/apps/readest-app/public/locales/fr/translation.json b/apps/readest-app/public/locales/fr/translation.json
index 7b85980e..96115e6e 100644
--- a/apps/readest-app/public/locales/fr/translation.json
+++ b/apps/readest-app/public/locales/fr/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "À propos de Readest",
   "Add your notes here...": "Ajoutez vos notes ici...",
   "Animation": "Animation",
+  "Apply": "Appliquer",
   "Are you sure to delete the selected books?": "Êtes-vous sûr de vouloir supprimer les livres sélectionnés ?",
   "Auto Mode": "Mode automatique",
   "Behavior": "Comportement",
diff --git a/apps/readest-app/public/locales/id/translation.json b/apps/readest-app/public/locales/id/translation.json
index 261b516f..89a09055 100644
--- a/apps/readest-app/public/locales/id/translation.json
+++ b/apps/readest-app/public/locales/id/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Tentang Readest",
   "Add your notes here...": "Tambahkan catatan Anda di sini...",
   "Animation": "Animasi",
+  "Apply": "Terapkan",
   "Are you sure to delete the selected books?": "Apakah Anda yakin ingin menghapus buku yang dipilih?",
   "Auto Mode": "Mode Otomatis",
   "Behavior": "Perilaku",
diff --git a/apps/readest-app/public/locales/it/translation.json b/apps/readest-app/public/locales/it/translation.json
index 2467827d..2aed8deb 100644
--- a/apps/readest-app/public/locales/it/translation.json
+++ b/apps/readest-app/public/locales/it/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Informazioni su Readest",
   "Add your notes here...": "Aggiungi qui le tue note...",
   "Animation": "Animazione",
+  "Apply": "Applica",
   "Are you sure to delete the selected books?": "Sei sicuro di voler eliminare i libri selezionati?",
   "Auto Mode": "Modalità automatica",
   "Behavior": "Comportamento",
diff --git a/apps/readest-app/public/locales/ja/translation.json b/apps/readest-app/public/locales/ja/translation.json
index e3fbe988..de999291 100644
--- a/apps/readest-app/public/locales/ja/translation.json
+++ b/apps/readest-app/public/locales/ja/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Readestについて",
   "Add your notes here...": "ここにメモを追加...",
   "Animation": "アニメーション",
+  "Apply": "適用",
   "Are you sure to delete the selected books?": "選択した書籍を削除してもよろしいですか？",
   "Auto Mode": "自動モード",
   "Behavior": "動作",
diff --git a/apps/readest-app/public/locales/ko/translation.json b/apps/readest-app/public/locales/ko/translation.json
index e0a5c456..b9286729 100644
--- a/apps/readest-app/public/locales/ko/translation.json
+++ b/apps/readest-app/public/locales/ko/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Readest 정보",
   "Add your notes here...": "여기에 메모를 추가하세요...",
   "Animation": "애니메이션",
+  "Apply": "적용",
   "Are you sure to delete the selected books?": "선택한 책을 삭제하시겠습니까?",
   "Auto Mode": "자동 모드",
   "Behavior": "동작",
diff --git a/apps/readest-app/public/locales/pt/translation.json b/apps/readest-app/public/locales/pt/translation.json
index e2efbebe..937fff28 100644
--- a/apps/readest-app/public/locales/pt/translation.json
+++ b/apps/readest-app/public/locales/pt/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Sobre o Readest",
   "Add your notes here...": "Adicione suas notas aqui...",
   "Animation": "Animação",
+  "Apply": "Aplicar",
   "Are you sure to delete the selected books?": "Tem certeza de que deseja excluir os livros selecionados?",
   "Auto Mode": "Modo Automático",
   "Behavior": "Comportamento",
diff --git a/apps/readest-app/public/locales/ru/translation.json b/apps/readest-app/public/locales/ru/translation.json
index f9a784f1..0e32a3d0 100644
--- a/apps/readest-app/public/locales/ru/translation.json
+++ b/apps/readest-app/public/locales/ru/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "О Readest",
   "Add your notes here...": "Добавьте свои заметки здесь...",
   "Animation": "Анимация",
+  "Apply": "Применить",
   "Are you sure to delete the selected books?": "Вы уверены, что хотите удалить выбранные книги?",
   "Auto Mode": "Автоматический режим",
   "Behavior": "Поведение",
diff --git a/apps/readest-app/public/locales/tr/translation.json b/apps/readest-app/public/locales/tr/translation.json
index 571d0afc..36dd4886 100644
--- a/apps/readest-app/public/locales/tr/translation.json
+++ b/apps/readest-app/public/locales/tr/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Readest Hakkında",
   "Add your notes here...": "Notlarınızı buraya ekleyin...",
   "Animation": "Animasyon",
+  "Apply": "Uygula",
   "Are you sure to delete the selected books?": "Seçili kitapları silmek istediğinizden emin misiniz?",
   "Auto Mode": "Otomatik Mod",
   "Behavior": "Davranış",
diff --git a/apps/readest-app/public/locales/vi/translation.json b/apps/readest-app/public/locales/vi/translation.json
index e002c3c0..fb2930c2 100644
--- a/apps/readest-app/public/locales/vi/translation.json
+++ b/apps/readest-app/public/locales/vi/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "Về Readest",
   "Add your notes here...": "Thêm ghi chú của bạn vào đây...",
   "Animation": "Hiệu ứng động",
+  "Apply": "Áp dụng",
   "Are you sure to delete the selected books?": "Bạn có chắc chắn muốn xóa các sách đã chọn?",
   "Auto Mode": "Chế độ tự động",
   "Behavior": "Hành vi",
diff --git a/apps/readest-app/public/locales/zh-CN/translation.json b/apps/readest-app/public/locales/zh-CN/translation.json
index 9e00524c..954b6f3a 100644
--- a/apps/readest-app/public/locales/zh-CN/translation.json
+++ b/apps/readest-app/public/locales/zh-CN/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "关于 Readest",
   "Add your notes here...": "在这里添加您的笔记...",
   "Animation": "动画",
+  "Apply": "应用",
   "Are you sure to delete the selected books?": "您确定要删除所选书籍吗？",
   "Auto Mode": "自动主题",
   "Behavior": "行为",
diff --git a/apps/readest-app/public/locales/zh-TW/translation.json b/apps/readest-app/public/locales/zh-TW/translation.json
index 0f45c41d..552160aa 100644
--- a/apps/readest-app/public/locales/zh-TW/translation.json
+++ b/apps/readest-app/public/locales/zh-TW/translation.json
@@ -2,6 +2,7 @@
   "About Readest": "關於 Readest",
   "Add your notes here...": "在這裡添加您的筆記...",
   "Animation": "動畫",
+  "Apply": "應用",
   "Are you sure to delete the selected books?": "您確定要刪除所選書籍嗎？",
   "Auto Mode": "自動主題",
   "Behavior": "行為",
diff --git a/apps/readest-app/src/app/reader/components/settings/MiscPanel.tsx b/apps/readest-app/src/app/reader/components/settings/MiscPanel.tsx
index 6fbdf553..56490fe0 100644
--- a/apps/readest-app/src/app/reader/components/settings/MiscPanel.tsx
+++ b/apps/readest-app/src/app/reader/components/settings/MiscPanel.tsx
@@ -1,13 +1,12 @@
+import clsx from 'clsx';
 import React, { useEffect, useState } from 'react';
 import { useReaderStore } from '@/store/readerStore';
 import { useSettingsStore } from '@/store/settingsStore';
 import { useTranslation } from '@/hooks/useTranslation';
-import cssbeautify from 'cssbeautify';
 import { getStyles } from '@/utils/style';
 import { useTheme } from '@/hooks/useTheme';
-
-const cssRegex =
-  /((?:\s*)([\w#.@*,:\-.:>+~$$$$\"=(),*\s]+)\s*{(?:[\s]*)((?:[^\}]+[:][^\}]+;?)*)*\s*}(?:\s*))/gim;
+import cssbeautify from 'cssbeautify';
+import cssValidate from '@/utils/css';
 
 const MiscPanel: React.FC<{ bookKey: string }> = ({ bookKey }) => {
   const _ = useTranslation();
@@ -18,44 +17,48 @@ const MiscPanel: React.FC<{ bookKey: string }> = ({ bookKey }) => {
 
   const [animated, setAnimated] = useState(viewSettings.animated!);
   const [isDisableClick, setIsDisableClick] = useState(viewSettings.disableClick!);
-  const [userStylesheet, setUserStylesheet] = useState(viewSettings.userStylesheet!);
+  const [draftStylesheet, setDraftStylesheet] = useState(viewSettings.userStylesheet!);
   const [error, setError] = useState<string | null>(null);
 
-  let cssInput = userStylesheet;
-
-  const validateCSS = (css: string) => {
-    return cssRegex.test(css);
-  };
-
   const handleUserStylesheetChange = (e: React.ChangeEvent<HTMLTextAreaElement>) => {
-    cssInput = e.target.value;
+    const cssInput = e.target.value;
+    setDraftStylesheet(cssInput);
 
     try {
-      const formattedCSS = cssbeautify(cssInput, {
-        indent: '  ',
-        openbrace: 'end-of-line',
-        autosemicolon: true,
-      });
-      setUserStylesheet(formattedCSS);
-
-      if (cssInput && !validateCSS(cssInput)) {
-        throw new Error('Invalid CSS');
+      const { isValid, error } = cssValidate(cssInput);
+      if (cssInput && !isValid) {
+        throw new Error(error || 'Invalid CSS');
       }
       setError(null);
-
-      viewSettings.userStylesheet = formattedCSS;
-      setViewSettings(bookKey, viewSettings);
-      if (isFontLayoutSettingsGlobal) {
-        settings.globalViewSettings.userStylesheet = formattedCSS;
-        setSettings(settings);
+    } catch (err: unknown) {
+      if (err instanceof Error) {
+        setError(err.message);
+      } else {
+        setError('Invalid CSS: Please check your input.');
       }
-      getView(bookKey)?.renderer.setStyles?.(getStyles(viewSettings, themeCode));
-    } catch (err) {
-      setError('Invalid CSS: Please check your input.');
       console.log('CSS Error:', err);
     }
   };
 
+  const applyStyles = () => {
+    const formattedCSS = cssbeautify(draftStylesheet, {
+      indent: '  ',
+      openbrace: 'end-of-line',
+      autosemicolon: true,
+    });
+
+    setDraftStylesheet(formattedCSS);
+    viewSettings.userStylesheet = formattedCSS;
+    setViewSettings(bookKey, viewSettings);
+
+    if (isFontLayoutSettingsGlobal) {
+      settings.globalViewSettings.userStylesheet = formattedCSS;
+      setSettings(settings);
+    }
+
+    getView(bookKey)?.renderer.setStyles?.(getStyles(viewSettings, themeCode));
+  };
+
   const handleInput = (e: React.FormEvent<HTMLTextAreaElement>) => {
     e.stopPropagation();
     e.nativeEvent.stopImmediatePropagation();
@@ -125,21 +128,31 @@ const MiscPanel: React.FC<{ bookKey: string }> = ({ bookKey }) => {
       <div className='w-full'>
         <h2 className='mb-2 font-medium'>{_('Custom CSS')}</h2>
         <div className={`card bg-base-100 border shadow ${error ? 'border-red-500' : ''}`}>
-          <div className='divide-y'>
-            <div className='css-text-area config-item-top config-item-bottom p-1'>
-              <textarea
-                className='textarea textarea-ghost h-48 w-full border-0 p-3 !outline-none'
-                placeholder={_('Enter your custom CSS here...')}
-                spellCheck='false'
-                value={cssInput}
-                onInput={handleInput}
-                onKeyDown={handleInput}
-                onKeyUp={handleInput}
-                onChange={handleUserStylesheetChange}
-              />
-            </div>
+          <div className='relative p-1'>
+            <textarea
+              className='textarea textarea-ghost h-48 w-full border-0 p-3 !outline-none'
+              placeholder={_('Enter your custom CSS here...')}
+              spellCheck='false'
+              value={draftStylesheet}
+              onInput={handleInput}
+              onKeyDown={handleInput}
+              onKeyUp={handleInput}
+              onChange={handleUserStylesheetChange}
+            />
+            <button
+              className={clsx(
+                'btn btn-ghost bg-base-200 absolute bottom-2 right-4 h-8 min-h-8 px-4 py-2',
+                !draftStylesheet ? 'hidden' : '',
+                error ? 'btn-disabled' : '',
+              )}
+              onClick={applyStyles}
+              disabled={!!error}
+            >
+              {_('Apply')}
+            </button>
           </div>
         </div>
+        {error && <p className='mt-1 text-sm text-red-500'>{error}</p>}
       </div>
     </div>
   );
diff --git a/apps/readest-app/src/utils/css.ts b/apps/readest-app/src/utils/css.ts
new file mode 100644
index 00000000..74c9e192
--- /dev/null
+++ b/apps/readest-app/src/utils/css.ts
@@ -0,0 +1,77 @@
+const cssValidate = (css: string) => {
+  // Remove comments and normalize whitespace
+  css = css.replace(/\/\*[\s\S]*?\*\//g, '').trim();
+
+  // CSS property pattern (validate both property name and value)
+  const propertyPattern = /^[\s\n]*[-\w]+\s*:\s*[^;]+;?$/;
+
+  // Check if empty
+  if (!css) return { isValid: false, error: 'Empty CSS' };
+
+  // Ensure balanced curly braces
+  const openBraces = (css.match(/{/g) || []).length;
+  const closeBraces = (css.match(/}/g) || []).length;
+  if (openBraces !== closeBraces) {
+    return { isValid: false, error: 'Unbalanced curly braces' };
+  }
+
+  // Split into rule blocks
+  const blocks = css
+    .split('}')
+    .map((block) => block.trim())
+    .filter(Boolean);
+
+  for (const block of blocks) {
+    // Ensure the block has a selector and declarations
+    const parts = block.split('{').map((part) => part.trim());
+    if (parts.length !== 2) {
+      return { isValid: false, error: 'Invalid CSS structure' };
+    }
+
+    const [selector, decls] = parts;
+
+    // Ensure selector is not empty
+    if (!selector) {
+      return { isValid: false, error: 'Missing selector' };
+    }
+
+    // Ensure declarations are not empty
+    if (!decls) {
+      return { isValid: false, error: `Missing declarations for selector: ${selector}` };
+    }
+
+    // Validate declarations
+    const props = decls
+      .split(';')
+      .map((prop) => prop.trim())
+      .filter(Boolean);
+
+    if (props.length === 0) {
+      return { isValid: false, error: `No valid properties for selector: ${selector}` };
+    }
+
+    for (const prop of props) {
+      // Check if property is missing a name or value
+      if (!prop.includes(':')) {
+        return { isValid: false, error: `Missing property or value: ${prop}` };
+      }
+
+      const [name, value] = prop.split(':').map((part) => part.trim());
+      if (!name) {
+        return { isValid: false, error: `Missing property name: ${prop}` };
+      }
+      if (!value) {
+        return { isValid: false, error: `Missing property value: ${prop}` };
+      }
+
+      // Validate full property format
+      if (!propertyPattern.test(prop.endsWith(';') ? prop : prop + ';')) {
+        return { isValid: false, error: `Invalid property: ${prop}` };
+      }
+    }
+  }
+
+  return { isValid: true, error: null };
+};
+
+export default cssValidate;