Optimize CSS

[captainbrosset]

Three possible improvements:

• Minify at build-time.
• Split into two main css files: lists of tips, content of a tip. These things aren't displayed at the same time, but we're always loading everything on all pages.
• Removed unused CSS. There's probably some of it somewhere, like

  .tips .tip.highlighted .highlight {
    background: var(--accent-color);
  }
  .tips.searching .tip:not(.highlighted) {
    display: none;
  }