It’s because of default macOS settings hijacking the shortcut. Go to System Settings → Keyboard → Keyboard Shortcuts and Input Sources. Uncheck the boxes.
Open Command Palette and choose "View: Reopen Editor with Text Editor"
CSS files should be interpreted as "tailwindcss" instead of CSS. Source. This made suggestions work, docs also work, and custom at-rules are also supported. It may require the PostCSS plugin.
settings.json
{
"tailwindCSS.experimental.configFile": "src/app/globals.css",
"files.associations": {
"*.css": "tailwindcss"
}
}
Things that are actually useful: