.box{--border-angle:0deg;border:5rem solid #0000;justify-content:center;align-items:center;animation:4s linear infinite border-angle-rotate;display:flex;position:relative}.box.b{background:conic-gradient(from var(--border-angle),var(--bg)50%,white)border-box}@keyframes border-angle-rotate{0%{--border-angle:0deg}to{--border-angle:360deg}}.orbit{--bg:#000;background:var(--bg)}@property --border-angle{syntax:"<angle>";inherits:false;initial-value:0deg}