fix: Make notification close button contrast for any theme #2241

[marek-mihok]

The PR fulfills these requirements: (check all the apply)

• [x] It's submitted to the main branch.
• [x] When resolving a specific issue, it's referenced in the PR's title (e.g. feat: Add a button #xxx, where "xxx" is the issue number).
• [x] When resolving a specific issue, the PR description includes Closes #xxx, where "xxx" is the issue number.
• [x] If changes were made to ui folder, unit tests (make test) still pass.
• [ ] New/updated tests are included

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Fix applies notification text color for the close icon.

Closes #2241