What version of Tailwind CSS are you using?

v4.0.10

What build tool (or framework if it abstracts the build tool) are you using?

Vite 6.2.0

What version of Node.js are you using?

v20.18.1

What browser are you using?

Chrome

What operating system are you using?

macOS

Reproduction URL

https://github.com/woohm402/tailwindcss-4.0.10-bug-reproduction-1

npm run dev and then visit http://localhost:5173 will work

Describe your issue

Using the legacy JavaScript config in v4.0.10, the theme font configuration with the name Title1_Strong does not generate a utility class, whereas Title_Strong does. In v4.0.9 and earlier versions, both utility classes were generated properly. The text-Title_Strong utility class is created, but text-Title1_Strong is not.

It appears that any font names following the \d_ pattern do not generate utility classes. However, other patterns such as Title1Strong and Title__Strong work properly.

tailwind config	created css