Fix: Optimized the table of contents style and homepage card layout #3221 (#9993)

### What problem does this PR solve?

Fix: Optimized the table of contents style and homepage card layout
#3221

- Added background color, text color, and shadow styles to the Markdown
table of contents
- Optimized the date display style in the HomeCard component to prevent
overflow
- Standardized the translation of "dataset" to "knowledge base" to
improve terminology consistency

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

web/src/components/api-service/chat-overview-modal/markdown-toc.tsx

@@ -53,14 +53,13 @@ const MarkdownToc: React.FC<MarkdownTocProps> = ({ content }) => {
 
   return (
     <div
-      className="markdown-toc"
+      className="markdown-toc bg-bg-base text-text-primary shadow shadow-text-secondary"
       style={{
         position: 'fixed',
         right: 20,
         top: 100,
         bottom: 150,
         width: 200,
-        background: '#fff',
         padding: '10px',
         maxHeight: 'calc(100vh - 170px)',
         overflowY: 'auto',