html,
body {
  font-family: 'UD 新ゴ R';
  font-size: 10px;
  font-size: clamp(1.0rem, 1vw, 2.0rem);
  height: 100%;
  margin: 0;
  padding: 0;
}

header {
  font-size: clamp(2.0rem, 2vw, 2.0rem);
  background-color: rgb(255, 255, 0);
  color: rgb(0, 128, 0);
  font-weight: bold;
  text-align: center;
}

nav {
  font-size: clamp(1.0rem, 1vw, 2.0rem);
  background-color: rgb(0, 128, 0);
  color: rgb(255, 255, 0);
  font-weight: bold;
  text-align: center;
}

footer {
  background-color: rgb(255, 255, 0);
  color: rgb(0, 128, 0);
  font-weight: bold;
  text-align: center;
}

h1 {
  font-weight: bold;
  color: red;
}

.image {
  max-width: 20vw;
  height: auto;
}

.contents {
  position: absolute;
  padding: 1rem;
}

.rainbow-top {
  width: 100vw;
  height: 5px;
  background-image: linear-gradient(to left, red, orange, yellow, green, cyan, blue, purple, red, orange, yellow, green, cyan, blue, purple, red);
  background-size: 200% 100%;
  animation: rainbow-top 5s ease-in-out infinite alternate;
}

.rainbow-bottom {
  width: 100vw;
  height: 5px;
  background-image: linear-gradient(to right, red, orange, yellow, green, cyan, blue, purple, red, orange, yellow, green, cyan, blue, purple, red);
  background-size: 200% 100%;
  animation: rainbow-bottom 5s ease-in-out infinite alternate;
}

@keyframes rainbow-top {
  0% {
    background-position: right;
  }

  100% {
    background-position: left;
  }
}

@keyframes rainbow-bottom {
  0% {
    background-position: left;
  }

  100% {
    background-position: right;
  }
}