From one line back to something editable
Shipped CSS is minified — every space and newline stripped to save bytes. That is great for the browser and unreadable for a human. Beautifying splits the rules and declarations back onto their own lines with consistent indentation, so you can read a compiled stylesheet or hand-edit a vendor file.
And back down again
Minify does the reverse: it strips comments and collapses whitespace to produce the smallest equivalent stylesheet, tightening the spacing around braces, colons and semicolons. Both directions run on your device, so nothing you paste is uploaded.