body {
  font-family: "Helvetica Neue", Arial, "Hiragino Kaku Gothic ProN", "Hiragino Sans", Meiryo, sans-serif;
  font-size: clamp(1rem, 0.9545454545rem + 0.2272727273vw, 1.125rem);
  background: #000;
}

.common-container {
  container: layout/inline-size;
  position: relative;
  width: 100%;
  max-width: 600px;
  margin: auto;
}
.common-container img {
  width: 100%;
}

a.btn {
  display: block;
  width: 180px;
  max-width: 30%;
  position: absolute;
  bottom: 6.1%;
  left: 50%;
  transform: translateX(-50%);
}
a.btn #progress-image {
  position: absolute;
  top: 0;
  left: 0;
}