CSS Selectors Level 1

E { /* rules */ }
E.class { /* rules */ }
E#id { /* rules */ }

E:link { /* rules */ }
E:visited { /* rules */ }
E:active { /* rules */ }

E F { /* rules */ }

CSS Selectors Level 2

* { /* rules */ }
E[foo] { /* rules */ }
E[foo="bar"] { /* rules */ }
E[foo~="bar"] { /* rules */ }
E[foo|="en"] { /* rules */ }
E:lang() { /* rules */ }

E:hover { /* rules */ }
E:focus { /* rules */ }
E:first-child { /* rules */ }
E > F { /* rules */ }
E + F { /* rules */ }

CSS Selectors Level 3

E[foo^="bar"] { /* rules */ }
E[foo$="bar"] { /* rules */ }
E[foo*="bar"] { /* rules */ }

E:enabled { /* rules */ }
E:disabled { /* rules */ }
E:checked { /* rules */ }
E:empty { /* rules */ }

E ~ F { /* rules */ }

:root { /* rules */ }

E:nth-child(n) { /* rules */ }
E:last-child { /* rules */ }
E:nth-last-child(n) { /* rules */ }
E:only-child { /* rules */ }

E:first-of-type { /* rules */ }
E:nth-of-type(n) { /* rules */ }
E:last-of-type { /* rules */ }
E:nth-last-of-type(n) { /* rules */ }
E:only-of-type { /* rules */ }

CSS Selevtors Level 3/4

E:not(s) { /* rules */ }
E:is(s) /*renamed :matches*/ { /* rules */ }

E:default { /* rules */ }

E:in-range { /* rules */ }
E:out-of-range { /* rules */ }
E:required { /* rules */ }
E:optional { /* rules */ }

E:read-only { /* rules */ }
E:read-write { /* rules */ }

CSS Selectors Level 4

E:dir(ltr) { /* rules */ }
E:any-link { /* rules */ }
E:local-link { /* rules */ }
E:local-link(0) { /* rules */ }

E:indeterminate { /* rules */ }

E:nth-match(n of s) { /* rules */ }
E:nth-last-match(n of s) { /* rules */ }

E:column(s) { /* rules */ }
E:nth-col(n) { /* rules */ }
E:nth-last-col(n) { /* rules */ }

will-change property

Old school

.accelerate {
    transform: translate3d(0, 0, 0);
}

Example

.will-change:active {
    will-change: transform;
    transition: transform 0.3s;
    transform: scale(1.5);
}

.will-change {
    transition: transform 0.3s;
}

.will-change:hover {
    will-change: transform;
}

.will-change:active {
    transform: scale(1.5);
}

Will-change on 'hover' event

.will-change-parent:hover .will-change {
    will-change: transform;
}

.will-change {
    transition: transform 0.3s;
}

.will-change:hover {
    transform: scale(1.5);
}

Don't forget to remove property

var el = document.querySelector('.element');

el.addEventListener('mouseenter', hintBrowser);
el.addEventListener('animationEnd', removeHint);

function hintBrowser() {
    this.style.willChange = 'transform';
}

function removeHint() {
    this.style.willChange = 'auto';
}