@import inserts another stylesheet's rules at that spot. It must precede every rule except @charset and @layer statements, and cannot sit inside @media; conditions follow the URL instead: layer() (Chrome 99 1 , Firefox 97 555 , Safari 15.4 10 ) puts the file into a cascade layer, supports() (Chrome 122, Firefox 115, Safari 17.5) requires a feature query to pass, and a media query list restricts devices.
@layer reset, vendor;
@import url("reset.css") layer(reset);
@import "bootstrap.min.css" layer(vendor);
@import "grid-layout.css" supports(display: grid) screen and (width >= 48rem);
@import "print.css" print;