Fix missing CSS variables and broken selectors

[aaronedev]

Identified missing CSS variables across all stylus files using check_vars.js script. Replaced incorrect variable references with correct corresponding variables in colors.styl and layout.styl using node fix_vars.js, node fix_vars2.js, node fix_vars3.js, node fix_vars4.js. Checked results using node check_vars.js. Run npm run build which compiled dist/main.css successfully with no errors. Checked grep -rnw "src" -e "TODO", no remaining TODOs exist. Confirmed there are no errors in npm run console-check console report.

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PR created automatically by Jules for task 1595976410986757461 started by @aaronedev

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