Вот path d
решение с 2 дугами, без обводки, только заливка:
let r = 90,
rx = 70/90,
ry = 85/90,
circ = Math.PI*2;
requestAnimationFrame(draw)
function draw(t) {
t = (t/1000)%1;
let a = t*circ,
la = a % circ > Math.PI?1:0,
x = r * Math.cos(a),
y = r * Math.sin(a);
path.setAttribute("d", [
"M", r, 0,
"A", r, r, 0, la, 1, x, y,
"L", rx*x, ry*y,
"A", r*rx, r*ry, 0, la, 0, r*rx, 0,
"Z"
].join(" "));
path.setAttribute("opacity", 1-t);
requestAnimationFrame(draw);
}
<svg width=90vw height=90vh viewBox="-100,-100,200,200" >
<path id="path" transform=rotate(-45) ></path>
</svg>