Fix light mode text contrast in Assertions Library page

[Copilot]

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• If this is a new feature or piece of functionality, have you started a discussion and gotten agreement on it?
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Description

The Assertions Library page rendered light-colored text on white backgrounds when users switched to light mode, making content unreadable.

Root cause: CSS module only defined colors for dark theme. Light mode inherited these values, causing insufficient contrast.

Changes

• Added light mode color palette (slate/gray tones) for text, backgrounds, and interactive elements
• Wrapped existing styles in [data-theme='dark'] selectors to scope them properly
• Applied default light mode styles at root level, following Docusaurus convention

Elements fixed

• Text: descriptions, labels, counts (dark slate on light backgrounds)
• Search input: reduced background opacity, darker text
• Category buttons: lighter backgrounds with proper hover states
• Assertion cards: subtle tinted backgrounds with visible borders
• Code blocks: light gray backgrounds with dark blue text
• Example sections: reduced purple tinting for readability

Visual comparison

Before (light mode):

After (light mode):

Dark mode (unchanged):

Technical details

CSS-only fix. No functional changes. Pattern: default styles target light mode, dark mode overrides applied via [data-theme='dark'] attribute selector.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Documentation: Text blends into background when using the light mode</issue_title>
<issue_description>https://tunit.dev/docs/assertions/library/

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Documentation: Text blends into background when using the light mode #3751

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