Radio Theme Swap

<!-- Radio Theme Swap — pure CSS via :has(); no JS required.
     :has() reads the checked radio and swaps the preview's color-scheme. -->
<div class="nuda-tt2-hasswap">
  <fieldset class="nuda-tt2-hasswap__fieldset">
    <legend class="nuda-tt2-hasswap__legend">Theme</legend>
    <label class="nuda-tt2-hasswap__opt" for="tt2-hasswap-light">
      <input class="nuda-tt2-hasswap__radio" type="radio" name="tt2-hasswap-theme" id="tt2-hasswap-light" checked />
      Light
    </label>
    <label class="nuda-tt2-hasswap__opt" for="tt2-hasswap-dark">
      <input class="nuda-tt2-hasswap__radio" type="radio" name="tt2-hasswap-theme" id="tt2-hasswap-dark" />
      Dark
    </label>
  </fieldset>
  <div class="nuda-tt2-hasswap__preview">
    <span class="nuda-tt2-hasswap__dot" aria-hidden="true"></span>
    Preview card
  </div>
</div>

.nuda-tt2-hasswap {
  display: inline-flex;
  flex-direction: column;
  gap: 10px;
  padding: 10px;
  background: rgba(255,255,255,.04);
  border: 1px solid rgba(255,255,255,.08);
  border-radius: 10px;
  color: #cfcfcf;
}

.nuda-tt2-hasswap__fieldset {
  display: flex;
  gap: 10px;
  border: none;
  margin: 0;
  padding: 0;
}

.nuda-tt2-hasswap__legend {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
}

.nuda-tt2-hasswap__opt {
  display: flex;
  align-items: center;
  gap: 6px;
  font: 600 11px ui-sans-serif,system-ui;
  cursor: pointer;
  min-height: 44px;
}

.nuda-tt2-hasswap__radio {
  width: 16px;
  height: 16px;
  accent-color: #e4ff54;
  cursor: pointer;
}

.nuda-tt2-hasswap__radio:focus-visible {
  outline: 2px solid #e4ff54;
  outline-offset: 2px;
}

.nuda-tt2-hasswap__preview {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 12px;
  border-radius: 8px;
  background: #fdf6e3;
  color: #3a3a1a;
  color-scheme: light;
  transition: background .4s ease,color .4s ease;
  font: 600 11px ui-sans-serif,system-ui;
}

.nuda-tt2-hasswap__dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: #f59e0b;
  transition: background .4s ease,box-shadow .4s ease;
}

.nuda-tt2-hasswap:has(#tt2-hasswap-dark:checked) .nuda-tt2-hasswap__preview {
  background: #141418;
  color: #e8e8ea;
  color-scheme: dark;
}

.nuda-tt2-hasswap:has(#tt2-hasswap-dark:checked) .nuda-tt2-hasswap__dot {
  background: #e4ff54;
  box-shadow: 0 0 8px rgba(228,255,84,.5);
}

@media (prefers-reduced-motion:reduce) {
  .nuda-tt2-hasswap__preview,.nuda-tt2-hasswap__dot {
    transition: none;
  }
}