CSS Minifier

It removes comments (except /*! … */ licence comments), collapses whitespace, drops spaces around braces, colons, semicolons, commas and child or sibling combinators, and removes the last semicolon in each rule. In property values it turns 0px into 0, 0.5em into .5em and #aabbcc into #abc. It does not rename anything, merge or reorder rules, remove empty rules, or touch selectors beyond their whitespace.

Those are the cases it is built to protect. Spaces inside calc(), min(), max() and clamp() are kept, and units inside them are never dropped, because calc(0px + 1px) is valid but calc(0 + 1px) is not. Quoted strings and unquoted url() values are carried through untouched, including any comment markers inside them. Media queries keep the space before each condition, and nested @media rules are handled like any other block.

Because it only shortens where the meaning cannot change. Zeros are left alone in custom properties (--gap: 0px), in the flex shorthand, and for units such as s, deg and %, where 0 is not always accepted in their place. Hex colors are only shortened in property values, never in selectors like #aabbcc, and values containing legacy progid: filters are skipped entirely.

No, and that is deliberate. Reformatting CSS reliably means knowing which commas separate selectors and which sit inside values, and getting that wrong changes the code. This page only minifies; use your editor's formatter or a dedicated beautifier to expand a stylesheet.

Use both. Minifying removes characters, while gzip or Brotli compression, which most servers apply automatically, shrinks repeating patterns. They stack, although the benefit of minifying is smaller once compression is on, so check the transfer size rather than just the raw size.

No. The minifier is JavaScript running in your browser, so a private theme or an unreleased design never leaves your device, and the tool keeps working offline once the page has loaded.