:root{--glow-accent:#000;--border-radius:16px;--trail-size:25;--speed:4s}.border-container{border-radius:var(--border-radius);clip-path:inset(0 0 0 0 round var(--border-radius));z-index:0;background:0 0;position:absolute;inset:-1.5px;overflow:hidden}.trail{aspect-ratio:2;background:radial-gradient(100% 100% at right,var(--glow-accent),transparent 50%);offset-path:border-box;offset-anchor:100% 50%;width:100px;animation:trailMove var(--speed)linear infinite;filter:drop-shadow(0 0 8px var(--glow-accent))brightness(1.3);position:absolute}@keyframes trailMove{to{offset-distance:100%}}html.light{--glow-accent:#000}html.dark{--glow-accent:#fff}