[Bug]: Inline HTML visuals show a dark-gray box against the black chat background #25907

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Use the default dark theme
2. Open any thread whose agent can call html_render
3. Have the agent show a visual whose page sets no background of its own
4. Look at the edges of the rendered visual in the chat

Expected behavior

The visual's background matches the chat background, so it blends into the conversation

Actual behavior

The visual draws a dark-gray (#0a0a0a) rectangle on the black (#000) chat background. Its edges stand out, and content that sits flush against them looks boxed in

Suspected cause:

• In dark mode, the chat background is --background: #000
• The visual's default canvas color is still canvas: "#0a0a0a"
• A comment next to the chat color says it was switched to true black. The visual's palette was not updated to match

Impact

Cosmetic issue

Version or commit

main @ 7c3b3b3 (still present at main @ 790ba13)

Environment

Windows 11 Pro, T3 Code desktop app, default dark theme

Logs or stack traces

Screenshots, recordings, or supporting files

82bbda1c-b9f4-478f-a45c-0afe6614fb48-91dfd7f9-c5b6-4af4-8fb2-07d816961209.png

Workaround

The page can set its own background to #000