s · ms
The second and the millisecond — the official time of transitions and animations.
One s is the ordinary second and one ms, its thousandth: the two currencies of the <time> type, spent on durations and delays of transition and animation. The border of good taste tends to live between them — microinteractions in hundreds of ms, long cycles in s.
One scale-room rigor sets them apart from lengths: zero needs its unit. margin: 0 clears inspection, but transition-duration: 0 is invalid — write 0s. Time, in this standard, never travels without papers.
.aviso {
transition: opacity 200ms ease-out;
}
.pulso {
animation: pulso 2s ease-in-out infinite alternate;
}