Unused CSS
Just like JavaScript, browsers download and parse all sent CSS, even rules that apply to no element on the page. This check measures the sav…
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How it works
How TheSiteFuse checks "Unused CSS"
Just like JavaScript, browsers download and parse all sent CSS, even rules that apply to no element on the page. This check measures the saveable KB. It's common with CSS frameworks loaded in full (Bootstrap, unpurged Tailwind) when only a few classes are used.
Why it matters
Real-world impact of "Unused CSS"
CSS is a render-blocking resource: the browser doesn't start displaying the page until all CSS has been parsed. Voluminous unused CSS directly delays FCP and LCP. PurgeCSS or modern frameworks' purge options can automatically remove unused rules.
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