* {
  box-sizing: border-box;
}
body {
  min-height: 100vh;
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
  align-items: center;
}

/* 装飾 */
a {
  color: #fff;
  background: #5876a3;
  padding: 10px 30px;
  display: inline-block;
  border-radius: 5px;
  text-decoration: none;
}