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dabblet.css

.pie {
	width: 200px;
	height: 200px;
	border-radius: 50%;
	background-color: black;
	border: 5px solid white;
	position: relative;
}

.pie:before,
.pie:after {
	width: 202px;
	height: 202px;
	border-radius: 50%;
	background-color: white;
	position: absolute;
	top: -1px;
	left: -1px;
	display: block;
	content: '';
	clip: rect(0, 101px, 202px, 0);
}


@keyframes piebefore {
	0% { rotate(-180deg)}
	50% { rotate(0deg) }
	100% { rotate(180deg)}
}




.pie:before {
        transform: rotate(-180deg);
        animation: piebefore;
}

body {
	background-color: black;
}

dabblet.html

<div class="pie">&nbsp;</div>

settings.json

{"view":"split-vertical","fontsize":"100","seethrough":"","prefixfree":"1","page":"css"}