Make result title highlighting more obvious in built-in themes

When searching, any returned result's title is highlighted where it matches the query,
However for most of the built in themes this effect is either so subtle its hard to notice or non existent.

This may be a subjective issue but I think it would be better to make this feature more obvious - especially on the default windows 11 theme

From the themes I tried it only seemed obvious on Sublime

Start by reproducing a search and comparing title highlighting across the built-in themes, especially the default Windows 11 theme and Sublime. Inspect the theme definitions and the search-result highlighting entry point; done means matching text is clearly visible in the affected themes without reducing readability.

Written by the indexing model from the issue text.