Fixed checkbox styling for dark mode: **Problem:** The bulk select checkboxes in the issues table (both header 'select all' and row checkboxes) were using default browser styling with white backgrounds that looked out of place in the dark theme. **Changes made:** Modified /tmp/trckr-TRCKR-227/server/templates/base.html (lines 144-188): - Added custom CSS for .issue-checkbox and #select-all-issues - Removed default appearance and styled with dark theme colors - Background: #0d1117 (matches page background) - Border: #30363d (matches other borders) - Checked state: #58a6ff background (accent blue) - Custom checkmark using CSS pseudo-element (::after) - Added hover state with blue border (#58a6ff) - Added focus outline for accessibility **Testing:** - Ran test suite: 1 test passed successfully - No regressions detected - CSS uses existing dark theme color palette for consistency **Implementation details:** - Used 'appearance: none' to remove browser default styling - Created custom checkmark with border-based CSS trick (rotated border) - 16x16px size for proper alignment in table cells - Hover and focus states for better UX - Consistent styling between header and row checkboxes