Make keywords bold.
Make attributes use a monospace font (like code).
Tweak light theme foreground colors:
* Make default-text, operator-text and punctuation-text a bit darker,
improving the contrast.
* Make builtin-text a bit darker and more green (similar to dark theme).
* Make function-text a bit darker and more greeny-blue (similar to dark
theme).
* Make attribute-text a bit less transparent for better contrast.
