fix: Add table row striping/borders and navigation active state styling

[AliMahmoudDev]

Summary

This PR fixes two frontend styling issues:

Table Styling - Row Striping and Borders (Closes #64)

• Added proper alternating row striping with distinct even/odd background colors (#f5f7fa / #ffffff)
• Added borders to all table cells (th and td) for clear data separation
• Styled the table header with a dark background (#333) and white text for better visual hierarchy
• Improved hover state with a blue highlight color (#e8f0fe) for better interactivity feedback
• Fixed the BUG comment that indicated missing row striping

Navigation Active State Styling (Closes #60)

• Added a prominent active state with blue background (#007bff) to clearly indicate the current page
• Added white text and bold font weight for the active navigation link
• Added a subtle box shadow for depth and visual emphasis
• Added hover state for the active link (#0056b3)
• Fixed a broken CSS rule that had color and padding properties outside of any selector (was a syntax error)

Testing

• Navigate between pages: the active link should be highlighted in blue
• View the Students table: rows should alternate between white and light gray
• Hover over table rows: should highlight in blue
• Table cells should have visible borders
• Table header should be dark with white text