Tailwind breakpoints

[Gachod-Pierre]

Hi everyone,

I'm currently building a WordPress theme using underscore-tw (_tw), which relies on Tailwind v4 and the CSS-first API (@tailwind, @theme, @layer base).
Typography, colors, spacing, and other tokens defined inside @theme { ... } work perfectly.

However, I’m running into a major issue:

➡️ I cannot get Tailwind breakpoints to work in _tw.

@screen sm { ... } → error: “The screen 'sm' does not exist in your theme config.”

Declaring breakpoints inside @theme (e.g. --breakpoint-sm: 640px) does not work

Creating a tailwind.config.js with theme.screens is also ignored

_tw seems to compile Tailwind only through the @tailwindcss/postcss plugin, without loading the full Tailwind engine or config file

So my questions are:

1. How are breakpoints supposed to be configured in underscore-tw?

Is there an official or recommended way to enable responsive utilities?

2. Is _tw expected to support Tailwind’s responsive features (@screen, sm:, md:, etc.)?

Or is responsive behavior intentionally unsupported in _tw?

3. What is the correct approach for implementing responsive typography / spacing in a _tw theme?

Should we rely entirely on plain CSS @media queries instead of Tailwind @screen?

Any explanation or guidance on how _tw handles (or doesn’t handle) breakpoints would be really appreciated.
Thanks in advance!

[gregsullivan]

Hi Pierre—Thanks for posting this!

There are a few things to cover here:

• @screen — To my knowledge this is deprecated; I'm not sure it was officially supported even in Tailwind 3.
• Breakpoints inside @theme — Make sure you use the same unit as the other breakpoints, or reset them before declaring them in other units. Tailwind uses rem by default.
• @tailwindcss/postcss — This isn't a partial version of Tailwind; it's simply Tailwind being loaded via PostCSS, so we can use PostCSS plugins.

With that preamble, you should be able to do everything covered in the Responsive design page in the v4 docs without modification. If you find that not to be the case, please let me know!