What do scrollbar-width: thin and scrollbar-color do?

scrollbar-width: thin gives a slimmer scrollbar in Firefox, and scrollbar-color sets the thumb and track colours in the order thumb then track.

Is anything uploaded?

No — the scrollbar CSS is generated entirely in your browser.

CSS Scrollbar Styler

Q: Why are there two sets of scrollbar rules?

Chrome, Edge and Safari use the ::-webkit-scrollbar pseudo-elements, while Firefox uses the standard scrollbar-width and scrollbar-color properties. The tool outputs both so your scrollbar styles work across browsers.

Style custom scrollbars and copy cross-browser CSS.

CSS scrollbar styler

Design a custom scrollbar and get cross-browser CSS. Set the width, corner radius and the track and thumb colours, then scroll the live preview to see it in action. The tool outputs the WebKit ::-webkit-scrollbar pseudo-elements for Chrome, Edge and Safari, plus the standard scrollbar-width and scrollbar-color properties for Firefox.

Everything runs in your browser — nothing is uploaded.