Tailwind config + plugins need to be migrated to v4 as CSS files. Colors in the config should be converted to oklch w/ the source hex as a comment, though we should look at whether we can rely on more of the built-in color palette and only provide the additional custom colors we need (I believe the built-in colors are a lot more saturated than our current custom ones, so if it doesn't look great let's stick with our custom ones).