Mozilla posted an interesting video about CSS @supports.
Examples:
/* If the browser supports CSS Grid, change the background color. */
@supports (display: grid) {
body: { background-color: green; }
}
/* Check if the browser supports the ::marker selector. */
@supports selector(::marker) {
body: { background-color: green; }
}
Browser support: https://caniuse.com/#feat=mdn-css_at-rules_supports_selector