This allows users to use #RRGGBBAA format in their style.css.
The client now detects 8-bit hex codes, transforms them into
GTK-compatible rgba() syntax, and loads the modified data
into the CSS provider.
- Added utility to detect 8-bit hex patterns.
- Added transformation logic to convert hex alpha to decimal.
- Intercepted CSS loading in Client::setupCss to handle the conversion.
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