main {
  font-family: "Noto Sans JP", sans-serif;
  font-weight: 300;
}
.relative {
  position: relative;
}
.absolute {
  position: absolute;
}
.float-btn {
  position: fixed;
  z-index: 100;
  bottom: -100vh;
  left: 50%;
  transform: translateX(-50%);
  max-width: 845px;
  width: 90%;
  transition: opacity 0.3s;
}
.float-btn.show {
  bottom: 10px;
}