<label class="radikalwp-theme-toggle">
  <input type="checkbox">
  <span class="radikalwp-theme-toggle__ball"><//span>
<//label>

.radikalwp-theme-toggle { display: inline-block; cursor: pointer; }
.radikalwp-theme-toggle input { display: none; }
.radikalwp-theme-toggle__ball {
  display: block;
  position: relative;
  width: 64px;
  height: 32px;
  background: linear-gradient(120deg, #fbbf24, #f59e0b);
  border-radius: 99px;
  transition: background .4s ease;
}
.radikalwp-theme-toggle__ball::before {
  content: '';
  position: absolute;
  top: 4px;
  right: 4px;
  width: 24px;
  height: 24px;
  background: #fff;
  border-radius: 50%;
  box-shadow: 0 0 12px rgba(251, 191, 36, .8);
  transition: transform .4s ease, box-shadow .4s ease;
}
.radikalwp-theme-toggle__ball::after {
  content: '';
  position: absolute;
  top: 9px;
  right: 32px;
  width: 14px;
  height: 14px;
  background: inherit;
  border-radius: 50%;
  opacity: 0;
  transition: opacity .3s;
}
.radikalwp-theme-toggle input:checked + .radikalwp-theme-toggle__ball { background: #1e293b; }
.radikalwp-theme-toggle input:checked + .radikalwp-theme-toggle__ball::before {
  transform: translateX(-32px);
  background: #e2e8f0;
  box-shadow: inset -5px -3px 0 0 #94a3b8;
}