body {
  background-color: #000;
  color: #fff;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  font-family: Helvetica, Arial, sans-serif;
  text-align: center;
}

.container {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  padding: 1rem;
}

.song-title {
  font-size: 2rem;
  cursor: pointer;
  position: relative;
  color: white;
  --progress: 0%;
  line-height: 1.2;
  display: inline-block;
  padding-bottom: 8px; /* extra space for thicker underline */
}

/* Red progress underline */
.song-title::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 0;
  height: 5px; /* increased thickness */
  width: var(--progress);
  background-color: red;
  transition: width 0.1s linear, opacity 0.4s ease;
  opacity: 0;
  pointer-events: none;
}

.song-title.playing::after {
  opacity: 1;
}