Web features we might not know
Web

Dialog
Container Query
Color Mix
:focus-visible
accessibility friendly way handle focus for form inputs and buttons.
.btn:focus-visible {
outline: 1px solid bisque;
}
.btn:focus:not(:focus-visible) {
outline: none;
}
Array Last Element
arr.at(-1); // the last element
Deep Clone
const newObj = structuredClone(oldObj);