Fix: Switch the default theme from light mode to dark mode and improve some styles #9869 (#10552)

### What problem does this PR solve?

Fix: Switch the default theme from light mode to dark mode and improve
some styles #9869
-Update UI component styles such as input boxes, tables, and prompt
boxes
-Optimize login page layout and style details
-Revise some of the wording, such as uniformly changing "data flow" to
"pipeline"
-Adjust the parser to support the markdown type

### Type of change

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

web/src/components/next-markdown-content/index.tsx

@@ -54,7 +54,10 @@ function MarkdownContent({
   const { setDocumentIds, data: fileThumbnails } =
     useFetchDocumentThumbnailsByIds();
   const contentWithCursor = useMemo(() => {
-    let text = DOMPurify.sanitize(content);
+    let text = DOMPurify.sanitize(content, {
+      ADD_TAGS: ['think', 'section'],
+      ADD_ATTR: ['class'],
+    });
     // let text = content;
     if (text === '') {
       text = t('chat.searching');