.p-anima-1 {
  background-color: #333;
  background-repeat: no-repeat;
  background-position: 100% 0;
  background-size: 200% auto;
  background-image: linear-gradient(to right, #6667ab 0%, #6667ab 50%, #333 50%, #333 100%);
  transition: color 0.4s, background-position 0.4s;
}
.p-anima-1:hover {
  background-position: 0 0;
}

/* アニメーションとは関係のないスタイル（ボタンの見た目など） */
body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}
.c-btn {
  display: block;
  color: #fff;
  font-size: 20px;
  font-weight: bold;
  text-align: center;
  background-color: #333;
  border-radius: 3px;
  width: 300px;
  margin: auto;
  padding: 20px 0;
	text-decoration: none;
}