<div class="wrapper">
  <header>
    <a href="#" class="fix-btn">問い合わせはこちら</a>
  </header>
  <div class="box">&nbsp;</div>
</div>
/*コンテンツ部分*/
.box{
  background:#ddd;
  width:100%;
  height:800px;
}
/*追従ボタン*/
.fix-btn{
  position:fixed;
  z-index:1;
  background:#2dd8c8;
  width:150px;
  border-radius:15px;
  text-decoration:none;
  font-size:14px;
  text-align:center;
  color:#333;
  padding:20px 0;
  right:20px;
  bottom:20px;
  box-shadow:1px 1px 5px #aaa;
}

External CSS

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External JavaScript

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