<div class="pie">0%</div>
<div class="pie">20%</div>
<div class="pie">40%</div>
<div class="pie">60%</div>
<div class="pie">80%</div>

.pie {
	display: inline-block;
	position: relative;
	width: 100px;
	line-height: 100px;
	border-radius: 50%;
	background: yellowgreen;
	background-image: linear-gradient(to right, transparent 50%, #655 0);
	color: transparent;
	text-align: center;
}

@keyframes spin {
	to { transform: rotate(.5turn); }
}
@keyframes bg {
	50% { background: #655; }
}   

.pie::before {
	content: '';
	position: absolute;
	top: 0; left: 50%;
	width: 50%; height: 100%;
	border-radius: 0 100% 100% 0 / 50%;
	background-color: inherit;
	transform-origin: left;
	animation: spin 50s linear infinite, bg 100s step-end infinite;
	animation-play-state: paused;
	animation-delay: inherit;
}

function $$(selector, context) {
	context = context || document;
	var elements = context.querySelectorAll(selector);
	return Array.prototype.slice.call(elements);
}

$$('.pie').forEach(function(pie) {
	var p = pie.textContent;
	pie.style.animationDelay = '-' + parseFloat(p) + 's';
});