css&svg

<style>
#svg1{
animation:ani1 12s infinite;
border:1px solid #000;
}

@keyframes ani1{
0%{
transform:rotateX(0deg) rotateY(0deg) rotateZ(0deg);
}50%{
transform:rotateX(0deg) rotateY(0deg) rotateZ(180deg);
}100%{
transform:rotateX(0deg) rotateY(0deg) rotateZ(0deg);
}}
</style>

<svg width="540" height="540" id="svg1">
<path d="m0 0L540 540" stroke="#000">
<animateTransform attributeName="transform" attributeType="xml" type="rotate" values="0 270 270; 360 270 270" begin="0s" dur="6s" repeatCount="indefinite"/>
</path>
</svg>