Change up styles of Homepage

[sawzedong]

Linked to issue #4

Previous

New

Changes

• Fixed margin errors where topics where being cut off by the screen.
• Topic headers now blur and have a slightly-transparent black overlay that is removed when hovered
• Gave the topic footers a different colour to appeal to the purple theme
• Gave background a light purple theme
• Moved the back-to-top button to a fixed position on the bottom right (this feels like a more accessible place to put it)

To note

• Database management topic was in the footer, and I moved it to the topics section and commented it out
• The background image for competitive coding becomes hard-to-see due to the overlay, maybe change to an image with higher contrast or adjust the overlay blur and opacity values