【CSS】脱jQueryでtransitionを使用してテキストの上にテキストカラーとは異なるカラーを走らせるアニメーションの実装方法のデモページ

body {
  background: #ddd;
}
.block {
  position: relative;
  margin: 70px 0 0;
  text-align: center;
  font-size: 50px;
}

.block div {
  overflow: hidden;
  width: 0;
}

.block div p {
  width: 100vw;
  word-wrap: break-word;
}

.block div:first-child {
  color: #fff;
  transition: width 1.5s cubic-bezier(0.2, 1, 0.2, 1), opacity 0.5s ease 1.5s;
}

.block div:nth-child(2) {
  position: absolute;
  left: 0;
  top: 0;
  transition: width 1.5s cubic-bezier(0.2, 1, 0.2, 1) 0.2s;
}

.block.active div {
  width: 100%;
}

.block.active div:first-child {
  opacity: 0;
  filter: alpha(opacity=0);
}

window.onload = function() {
  document.getElementById("block").classList.add("active")
};