<div class="box"></div>

html, body {
  height: 100%;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  background: #333;
}

.box {
  width: 150px;
  height: 150px;
  background: red;
  transition: 
    /* step 1 */
    width      1s,
    /* step 2 */
    background 0.5s 1s;
}

.box:hover {
  width: 300px;
  background: orange;
}