<div class="btn first">
  Кнопка
</div>

<div class="btn second">
  <div class="text">Кнопка два</div>
</div>

.text {
  position: relative;
  z-index: 2;
}

.btn {
  display: inline-block;
  padding: 10px 15px;
  color: #fff;
  cursor: pointer;
  overflow: hidden;
  transition: 0.35s;
}

.btn.first {
  background-color: red;
}

.btn.second {
  background-color: green;
  position: relative;
}

.btn.first:hover {
  background-color: yellow;
  color: #000;
}

.btn.second:after {
  content: '';
  width: 100%;
  height: 100%;
  background-color: blue;
  position: absolute;
  top: 0;
  left: 0;
  transform: translateX(100%);
  transition: 0.35s;
}

.btn.second:hover:after {
  transform: translateX(0);
}