fix: Fix markdown lazy load preview message background color

[chohongm]

Changes

• Fixed markdown lazy load preview message background color

ticket: AC-4525

Additional Notes

Checklist

Before requesting a code review, please check the following:

• [Required] CI has passed all checks.
• [Required] A self-review has been conducted to ensure there are no minor mistakes.
• [Required] Unnecessary comments/debugging code have been removed.
• [Required] All requirements specified in the ticket have been accurately implemented.
• Ensure the ticket has been updated with the sprint, status, and story points.

[netlify]

✅ Deploy Preview for chat-ai-widget ready!

Name	Link
🔨 Latest commit	ada6fdf
🔍 Latest deploy log	https://app.netlify.com/sites/chat-ai-widget/deploys/675aa74337b57400087a318a
😎 Deploy Preview	https://deploy-preview-401--chat-ai-widget.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[github-actions]

Size Change: -57 B (-0.01%)

Total Size: 618 kB

Filename	Size	Change
./dist/__bundle-46d64517-********.js	4.01 kB	+2 B (+0.05%)
./dist/__bundle-b5ef7de4-********.js	890 B	-1 B (-0.11%)
./dist/index-********.js	304 kB	+25 B (+0.01%)
./dist/index.es.js	170 B	-2 B (-1.16%)
./dist/index.umd.js	289 kB	-27 B (-0.01%)
./dist/Placeholder.noChannels-********.js	182 B	-1 B (-0.55%)
./dist/style.css	9.61 kB	+8 B (+0.08%)
./dist/TokensBody-********.js	9.1 kB	-61 B (-0.67%)

ℹ️ View Unchanged

Filename	Size
./dist/__bundle-7c3d40f4-********.js	21 B
./dist/Placeholder.error-********.js	345 B
./dist/Placeholder.loading-********.js	184 B
./dist/Placeholder.noMessages-********.js	183 B
./dist/PlaceholderCommon-********.js	245 B

_{compressed-size-action}