This gist may be your full solution or just the starting point for making your Tailwind v4 projects backwards compatible.
- Effectively getting browser support down to Chrome 99 (and basically everything supporting 
@layer) - Pre-compute 
oklab()functions - Pre-compute 
color-mix()functions (+ replace CSS vars inside them beforehand) - Remove advanced instructions (colorspace) from gradients
 - Provide support for nested CSS (used by dark mode or custom variants with 
&) - Transform 
translate,scale,rotateproperties to theirtransform: ...notation - Add whitespace to var fallbacks 
var(--var,)>var(--var, )to help older browsers understand