Since 1.43, VSCode themes can take advantage of semantic highlighting.

Every theme controls whether semantic tokens are enabled. So far, only built-in themes have it enabled and I filed this issue to ask you to opt-in for the ayu theme as well.

Adoption is easy and there are new cool styling possibilities.

To turn on semantic highlighting for a theme, all you have to do is put
"semanticHighlighting": true
in the theme's definition file.

There's a good chance that no further change to the theme is needed (thanks to a default mapping from semantic tokens to TextMate scopes (if not, I'd be interested to know, so I can improve the defaults further)).

But, more interestingly, themes can tune and go wild by defining new styling rules against the semantic tokens:

"semanticTokenColors": {
    "variable.readonly": "#ff0000", 
    "parameter": { "fontStyle": "underline" },
    "*.declaration:java": { "fontStyle": "bold" }
} 

Check out our Semantic Highlighting Wiki and the Semantic Highlighting Guide for more details and feel free to ping me in this issue if I can help.

Thanks for the great work and looking forward to semantic highlighting in your theme.