* refactor: CSS variables to use fixit-var for consistency across styles
* refactor: reorganize CSS structure and consolidate imports for improved maintainability
* refactor: unify CSS variable usage and improve structure across stylesheets
* refactor: standardize CSS variable usage for layout
* refactor: standardize CSS variable usage for archive and special pages
* refactor: standardize CSS variable usage for single page
* refactor: standardize CSS variable usage for widgets
* refactor(css): refactors the border-radius mixin and adds the .rounded-full utility class
* refactor: standardize z-index usage across components
* refactor(css): removes deprecated compatibility mixins and replaces them with native CSS properties
* feat: unify color variable naming and update theme color values
- Rename `global-font-secondary-color` to `global-placeholder-color` for more accurate description of its purpose
- Update multiple style references to use the new `secondary` theme color variable
- Update theme color mapping to the new color values for improved visual consistency
- Fixed the use of search box placeholder colors and removed hard-coded transparency values
- Added color preview test documentation for easier verification of color rendering
- Cleaned up some duplicate dark mode styles and replaced them with unified CSS variables
* refactor: remove the `hr-background-color` variable and uses `global-border-color` uniformly
* feat(CSE): add dark theme style to Google CSE search box and results container
* fix(task-lists): fixed styling and rendering issues with nested task lists
* feat: add toc drawer button
* feat: add TOC dialog functionality and related styles
* feat: change back-to-top button with scroll progress indicator
* feat: update color-scheme handling in theme switcher
* fix: code review for checking mistakes and optimization
* fix: the issue where the TOC was still clickable even when it was hidden.
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