<fieldset class="crb-neon">
  <legend class="crb-sr">Mode</legend>
  <label><input type="radio" name="crb-neon" /><span></span>Idle</label>
  <label><input type="radio" name="crb-neon" checked /><span></span>Active</label>
  <label><input type="radio" name="crb-neon" /><span></span>Burst</label>
</fieldset>

.crb-neon { display: flex; flex-direction: column; gap: 10px; border: 0; padding: 0; }
.crb-neon label {
  display: flex; align-items: center; gap: 10px;
  font: 500 13px/1 monospace; color: #b8b6d4; cursor: pointer;
}
.crb-neon input { appearance: none; -webkit-appearance: none; position: absolute; opacity: 0; }
.crb-neon span {
  width: 16px; height: 16px; border-radius: 50%;
  border: 1.5px solid #2a4a3a; background: transparent;
  position: relative;
  transition: border-color 0.25s, box-shadow 0.3s;
}
.crb-neon span::after {
  content: ''; position: absolute; inset: 3px;
  border-radius: 50%; background: #2ecc8a;
  opacity: 0; transform: scale(0.4);
  transition: opacity 0.25s, transform 0.3s;
}
.crb-neon input:checked + span {
  border-color: #2ecc8a;
  box-shadow: 0 0 12px rgba(46,204,138,0.6), inset 0 0 6px rgba(46,204,138,0.3);
}
.crb-neon input:checked + span::after {
  opacity: 1; transform: scale(1);
  box-shadow: 0 0 6px #2ecc8a;
}

.crb-sr {
  position: absolute !important;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}