Usually 20–30% of the raw bytes, more on a heavily commented stylesheet. After gzip the difference narrows considerably, because compression already handles repeated whitespace well — but the parse cost of the smaller file is genuinely lower.

Will it break my CSS?

It preserves everything semantic — selectors, properties, values, media queries and the cascade order. Comments go, including any licence header you need to keep, so extract those first if your dependencies require attribution.

Does it remove unused rules?

No. That is a different job and a far riskier one — removing unused CSS requires knowing every class your JavaScript might add at runtime. This only removes bytes that no parser needs.

CSS Minifier

Remove comments, whitespace and the last semicolon in each block to shrink a stylesheet, typically by 20–30%. Paste CSS, copy the minified output. Runs entirely in your browser — nothing about your design system is uploaded.

Runs in your browser — nothing is uploaded

Questions

How much can I save?: Usually 20–30% of the raw bytes, more on a heavily commented stylesheet. After gzip the difference narrows considerably, because compression already handles repeated whitespace well — but the parse cost of the smaller file is genuinely lower.
Will it break my CSS?: It preserves everything semantic — selectors, properties, values, media queries and the cascade order. Comments go, including any licence header you need to keep, so extract those first if your dependencies require attribution.
Does it remove unused rules?: No. That is a different job and a far riskier one — removing unused CSS requires knowing every class your JavaScript might add at runtime. This only removes bytes that no parser needs.