Redesigned the color scheme from one blue to five different colors

- Added new design elements for the new color schemes: grey for the
front page, yellow for activities, green for tales, blue for rhymes and
red for songs.
- Implemented the grey color scheme for the front page
Added styling for the yellow scheme (activities) and styled the menu with each category's color
Added styling for the green scheme (tales)
Added styling for the blue scheme (rhymes)
Added styling for the red scheme (songs)
Corrected the switched colors in the new color schemes
Optimized navigation styling
Added color scheme styles to tablet.css
Added color scheme styles to phone.css
Removed unnecessary no-repeats