Snap-to-Grid Placement

<!-- Snap-to-Grid Placement — the target marks the nearest cell while the
     block is dragged; drop snaps the block to that cell's coordinates.
     Keyboard: focus the block, Alt+Arrow keys move it one cell at a time. -->
<div class="nuda-dd2-snap-grid">
  <p id="dd2-snap-grid-desc" class="nuda-dd2-snap-grid__sr">Drag the block onto the grid to snap it into place, or focus it and press Alt plus Arrow keys to move it one cell at a time.</p>
  <div class="nuda-dd2-snap-grid__canvas" role="application" aria-label="Snap to grid canvas" aria-describedby="dd2-snap-grid-desc">
    <div class="nuda-dd2-snap-grid__target" aria-hidden="true"></div>
    <div class="nuda-dd2-snap-grid__block" role="button" tabindex="0" aria-label="Block, draggable">▮</div>
  </div>
</div>

.nuda-dd2-snap-grid {
  width: 160px;
}

.nuda-dd2-snap-grid__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}

.nuda-dd2-snap-grid__canvas {
  position: relative;
  width: 160px;
  height: 100px;
  border-radius: 10px;
  border: 1px solid rgba(255,255,255,.08);
  background-image: linear-gradient(rgba(255,255,255,.06) 1px,transparent 1px),linear-gradient(90deg,rgba(255,255,255,.06) 1px,transparent 1px);
  background-size: 20px 20px;
  background-color: #101010;
}

.nuda-dd2-snap-grid__target {
  position: absolute;
  left: 100px;
  top: 60px;
  width: 36px;
  height: 36px;
  border: 1.5px dashed rgba(228,255,84,.5);
  border-radius: 6px;
  animation: nuda-dd2-snap-grid-target 3s ease-in-out infinite;
}

.nuda-dd2-snap-grid__block {
  position: absolute;
  left: 20px;
  top: 20px;
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #e4ff54;
  color: #0a0a0a;
  border-radius: 6px;
  font: 700 14px ui-sans-serif,system-ui;
  cursor: grab;
  animation: nuda-dd2-snap-grid-move 3s cubic-bezier(.4,0,.2,1) infinite;
}

.nuda-dd2-snap-grid__block:focus-visible {
  outline: 2px solid #fafafa;
  outline-offset: 2px;
}

@keyframes nuda-dd2-snap-grid-move {
  0%,10% {
    transform: translate(0,0) scale(1);
  }
  40% {
    transform: translate(80px,40px) scale(1.12);
  }
  55% {
    transform: translate(80px,40px) scale(.95);
  }
  65%,90% {
    transform: translate(80px,40px) scale(1);
  }
  100% {
    transform: translate(0,0) scale(1);
  }
}

@keyframes nuda-dd2-snap-grid-target {
  0%,10%,100% {
    opacity: .35;
  }
  40%,90% {
    opacity: 1;
  }
}

@media (prefers-reduced-motion:reduce) {
  .nuda-dd2-snap-grid__block {
    animation: none;
    transform: translate(80px,40px);
  }
  .nuda-dd2-snap-grid__target {
    animation: none;
    opacity: 1;
  }
}