Fix perps chart dark mode flicker

[dylanbutler1]

Fix TAT-1563: Prevent Perps Chart loading state from flickering white in dark mode by adjusting container and WebView backgrounds.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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[github-actions]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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