<!DOCTYPE html>
<html lang="ja">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/meyer-reset/2.0/reset.min.css">
<style>@charset "utf-8";

/*角丸に変わる*/
.btnchangeradius {
  display: inline-block;
  margin: 20px 0;
  text-decoration: none;
  outline: none;
  font-size: max(14px, 2vw);
  white-space: nowrap;
  width: max(150px, 40vw);

  background: #333;
  color: #fff;
  padding: 10px 20px;
  border: 5px double white;

  /*アニメーションの指定*/
  transition: 0.3s ease-out;
}

/*hoverした際の角丸のアニメーション*/
.btnchangeradius:hover {
  background: #666;
  border-radius: 50px;
}

/*========= レイアウトのためのCSS ===============*/

body {
  width: 100%;
  height: 100vh;
  vertical-align: middle;
  padding: 30px 0;
  text-align: center;

  background-repeat: no-repeat;
  background-position: center;
  background-size: cover;

  background-image: linear-gradient(
    103.3deg,
    rgba(252, 225, 208, 1) 30%,
    rgba(255, 173, 214, 1) 55.7%,
    rgba(162, 186, 245, 1) 81.8%
  );
}

/*ボタンの配置*/
.btn-position {
  display: flex;
  flex-direction: column;
  align-items: center;
}

p {
  margin: 0 0 10px 0;
}</style>
</head>
<body>
<body>
<div class="btn-position">
<a href="#" class="btnchangeradius">角丸に変わる</a>
</div>
<script>
</script>
</body>
</html>
/* 
   外部依存 CSS:
     - https://cdnjs.cloudflare.com/ajax/libs/meyer-reset/2.0/reset.min.css
 */

@charset "utf-8";

/*角丸に変わる*/
.btnchangeradius {
  display: inline-block;
  margin: 20px 0;
  text-decoration: none;
  outline: none;
  font-size: max(14px, 2vw);
  white-space: nowrap;
  width: max(150px, 40vw);

  background: #333;
  color: #fff;
  padding: 10px 20px;
  border: 5px double white;

  /*アニメーションの指定*/
  transition: 0.3s ease-out;
}

/*hoverした際の角丸のアニメーション*/
.btnchangeradius:hover {
  background: #666;
  border-radius: 50px;
}

/*========= レイアウトのためのCSS ===============*/

body {
  width: 100%;
  height: 100vh;
  vertical-align: middle;
  padding: 30px 0;
  text-align: center;

  background-repeat: no-repeat;
  background-position: center;
  background-size: cover;

  background-image: linear-gradient(
    103.3deg,
    rgba(252, 225, 208, 1) 30%,
    rgba(255, 173, 214, 1) 55.7%,
    rgba(162, 186, 245, 1) 81.8%
  );
}

/*ボタンの配置*/
.btn-position {
  display: flex;
  flex-direction: column;
  align-items: center;
}

p {
  margin: 0 0 10px 0;
}
/* 
   外部依存 CSS (このデモは下記の CSS にも依存します):
     - https://cdnjs.cloudflare.com/ajax/libs/meyer-reset/2.0/reset.min.css
 */