Implement dark and light mode toggle and enhance border visibility in dark mode

The application currently lacks a proper dark and light mode switch. Additionally, in dark mode, the borders are barely visible, making the UI elements blend into the background.

Tasks:

Implement a theme toggle feature (dark/light mode).

Ensure that border colors are properly adjusted for visibility in dark mode.

Maintain consistent UI styling and contrast across both themes.

Expected Behavior:

Users should be able to switch between dark and light modes seamlessly.

Borders and outlines should remain clearly visible and consistent in both modes.