Preserve alpha component when applying custom styles
Description
Alpha component from a color in our style was previously dropped when applying an app's style modifications.
Screenshots
Technical details
Alpha is now re-added to the color after the modification operation is complete, as it is dropped when extracting hsl values.
Tests
Issues
- https://gitlab.e.foundation/e/os/backlog/-/issues/915
- adjacent: https://gitlab.e.foundation/e/os/backlog/-/issues/1507