docs(sidebar): improve readability and contrast at 910px

[shhreya13]

This PR improves the readability and visual hierarchy of the documentation sidebar for medium-width viewports (~768px to 991px). It addresses specifically reported issues regarding small font sizes, cramped spacing, and low text contrast at approximately 910px.

Changes
Typography: Increased the base font size for menu items to 14px and sub-menu items to 13px to improve legibility on dark backgrounds.

Spacing: Adjusted line-height to 1.6 and increased vertical padding to 0.9em to reduce visual density and improve the interactive "hit area" for navigation links.

Visual Hierarchy: Enhanced section headers (e.g., "Elements", "Collections") by increasing font size to 1.1em and setting color to pure white (#fff).

Accessibility: Increased the text contrast of nested menu items to rgba(255, 255, 255, 0.8) to ensure compliance with WCAG AA standards for text on dark backgrounds.

Responsive Design: Implemented these changes via a targeted @media query in docs/src/Style.js to ensure the layout remains balanced as the viewport scales.

Environment
Version: 3.0.0-beta.2

Tested on: Chrome 130 (Windows 11) at ~910px

[vercel]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.53%. Comparing base (e0a42b5) to head (676d28c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4534   +/-   ##
=======================================
  Coverage   99.53%   99.53%           
=======================================
  Files         186      186           
  Lines        3463     3463           
=======================================
  Hits         3447     3447           
  Misses         16       16           

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