.radio-stack {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: 12px;
  padding: 12px;
  background: #0f172a;
  border-radius: 12px;
  width: 200px;
  font-family: sans-serif;
}

.radio-stack input {
  display: none;
}

.radio-stack label {
  position: relative;
  padding: 12px 16px;
  padding-right: 40px;
  color: #94a3b8;
  background: #1e293b;
  border-radius: 8px;
  cursor: pointer;
  transition: background 0.3s ease, color 0.3s ease;
  z-index: 1;
}

.radio-stack label:hover {
  background: #334155;
}

.radio-stack .ball {
  content: "";
  position: absolute;
  width: 20px;
  height: 20px;
  background: #38bdf8;
  border-radius: 50%;
  right: 24px;
  opacity: 0;
  transform: scale(0.6) translateX(0px);
  transition: all 0.3s ease;
  z-index: 2;
}

#opt1:checked ~ .ball {
  top: 26px;
  opacity: 1;
  transform: scale(1) translateX(8px);
}
#opt2:checked ~ .ball {
  top: 86px; 
  opacity: 1;
  transform: scale(1) translateX(8px);
}
#opt3:checked ~ .ball {
  top: 146px;
  opacity: 1;
  transform: scale(1) translateX(8px);
}

/* 선택된 라벨 강조 */
#opt1:checked ~ label[for="opt1"],
#opt2:checked ~ label[for="opt2"],
#opt3:checked ~ label[for="opt3"] {
  background: #334155;
  color: white;
}