Does it detect repeated colors automatically?

Yes. Colors appearing more than once are extracted and a generated --color-name variable is proposed.

Can I name the variables myself?

Yes. Auto-generated names are editable before you copy the output.

Yes. Hex, rgb(), rgba(), hsl(), and named colors are all detected and extracted.

An SCSS mode generates $variable syntax instead of CSS custom properties if preferred.

Paste CSS and have repeated values extracted into --custom-property declarations automatically.

demo

CSS Output