fix(ui-mode): properly color checkboxes and scrollbars with diff themes

[agg23]

In UI Mode, manually changing the color theme to be different from the OS's theme can produce strange color artifacts. For example, with macOS in dark theme, with the UI in light theme, the checkboxes and scrollbars will appear dark. Resolve this issue.

After

Before

[github-actions]

Test results for "tests 1"

4 flaky

⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:1079 › cli codegen › should not throw csp directive violation errors `@firefox-ubuntu-22.04-node18`
⚠️ [firefox-page] › page/page-wait-for-function.spec.ts:104 › should work with strict CSP policy `@firefox-ubuntu-22.04-node18`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:397 › should work behind reverse proxy `@macos-latest-node18-1`
⚠️ [webkit-library] › library/inspector/cli-codegen-aria.spec.ts:76 › should update aria snapshot highlight `@webkit-ubuntu-22.04-node18`

46674 passed, 817 skipped

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Merge workflow run.