fix: improve dark mode card contrast and elevation hierarchy

[ni2-vsv11]

Summary

Improved dark mode elevation hierarchy by increasing contrast between background, card, and muted card surfaces.

Changes Made

• Updated --card color from #0e0e0e to #111111
• Updated --card-muted color from #161616 to #1a1a1a
• Updated --border color from #222222 to #2a2a2a

Impact

• Better visual separation between page background and cards
• Improved readability and layout clarity in dark mode
• Enhanced elevation hierarchy on IPS/non-OLED displays
• More visible borders for dashboard widgets, settings sections, and leaderboard rows

Tested

• Dashboard
• Settings page
• Leaderboard
• Dark mode across different screen sizes

Closes #1067

[vercel]

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the global theme color variables to adjust dark-mode surface and border tones for improved visual consistency.

Changes:

• Tweaked --card background color to a slightly lighter value.
• Adjusted --card-muted and --border colors to new dark gray values.

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