Migrate UI to shared components

[jeluard]

Also relates to #123

[jeluard]

Take this as an opportunity to use CSS variable for easier customization.

• https://tailwindcss.com/docs/customizing-colors#using-css-variables
• https://tailwindcss.com/blog/tailwindcss-v3-1#easier-css-variable-color-configuration
• https://tailwindcss.com/docs/adding-custom-styles
• https://www.youtube.com/watch?v=MAtaT8BZEAo

And introduce dark mode

[dnlklmn]

i can export all styles (dark and light mode, global and semantic) from figma to css variables, lmk when you get there