docs: More fixes to the overview page in light mode

[desmondcheongzx]

Changes Made

Apparently if your system settings is in dark mode, this interacted strangely with our docs.

[greptile-apps]

Greptile Summary

This PR fixes CSS styling issues in the documentation overview page (docs/index.md) that were causing display problems when users had dark system settings but were viewing the documentation in light mode. The change completely restructures the CSS approach from using CSS custom properties (variables) to hardcoded color values.

The original implementation used CSS variables like --daft-text-color and --daft-bg-color to create a maintainable theming system. However, this variable-based approach was apparently not behaving correctly in certain browser/system combinations, particularly when system preferences were set to dark mode but the documentation was being viewed in light mode.

The fix involves three main changes:

1. Removing all CSS custom property declarations and replacing them with direct color values (e.g., color: #1a1a1a instead of color: var(--daft-text-color))
2. Duplicating dark mode styles for both system preference dark mode (@media (prefers-color-scheme: dark)) and Material for MkDocs slate theme ([data-md-color-scheme="slate"])
3. Maintaining the same visual appearance but with more explicit, predictable color definitions

This change ensures consistent rendering across all viewing scenarios by explicitly defining styles for each mode rather than relying on CSS variables that may not cascade properly in certain configurations. The documentation structure and content remain unchanged - this is purely a CSS implementation detail that improves cross-browser compatibility.

Confidence score: 5/5

• This PR is safe to merge with minimal risk as it only affects CSS styling in documentation
• Score reflects that this is a low-risk documentation-only change with no impact on application logic
• No files require special attention - this is a straightforward CSS fix

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