This feature, when used with a new enough Tailwind CSS version (v4.1.15+), allows IntelliSense to detect when a utility you've written could be written in a more succinct / optimal fashion. These suggestions are unique to your project so if you customize your theme that will be taken into account.

It can suggest utilities that match arbitrary ones:

It can also match arbitrary values against values in your theme:

This includes matching against custom theme values in your project:

It even works for variants:

And of course it works for both simultaneously:

When presented with one of these diagnostics it will also have an accompanying code action that lets you replace the class:

Note: Matching is done with mostly exact values to your theme so colors that parse to the same value but don't match won't necessarily be suggested. This is a possible future improvement but requires some design work in Tailwind CSS itself.