Awake

Here’s a way to do this using CSS variables:

<div style="--from-width:10px; --to-width:20px; animation: load 3s normal forwards;"></div>

OR

<div style="--from-width:10px; --to-width:20px;" class="animation"></div>

.animation {
animation: load 3s normal forwards;
}

@keyframes load {
  from {
    width: var(--from-width);
  }

  to {
    width: var(--to-width);
  }
}