Clean up and refactor CSS

[gordlin]

Description

After all the recent code refactors, the CSS has become fragmented, with repeated implementations, duplicate stylings, and other issues that make it hard to debug and refactor the codebase stylings.

Is your feature request related to a problem?

Doing this now === less styling nightmares later.

Proposed solution

After #486, #489, and #499 are merged, clean up and unify the codebase CSS.

• Most common element styles (e.g. buttons, inputs) can be added to the main CSS file.
• Many repeated tailwind stylings can be modularized into CSS classes.
• Create new reusable Vue components for more complex, but repeatedly used, UI items.
• Anything else that cleans stuff up.

Related issues

#503, #504