<div class="stack-bounce">
<span></span><span></span><span></span>
</div>
<style>
.stack-bounce { display:grid; gap:8px; width:120px; }
.stack-bounce span{
height:10px; border-radius:8px;
background: linear-gradient(135deg,#5b8def,#9a6bff);
box-shadow:0 6px 18px rgba(91,141,239,.2);
animation: stack-bounce 1s ease-in-out infinite;
}
.stack-bounce span:nth-child(2){animation-delay:.12s;}
.stack-bounce span:nth-child(3){animation-delay:.24s;}
@keyframes stack-bounce{0%,100%{transform:translateY(0);opacity:.85;}50%{transform:translateY(-8px);opacity:1;}}
</style>