div {
  width: 100px;
  height: 100px;
  background: red;
  transition: width 2s, height 4s;
}

div:hover {
  width: 300px;
  height: 300px;
}

HTML

Voor meer details surf je naar css3_transition.

<button>
  This Button
  <span>is Cool.</span>
</button>
@import url(https://fonts.googleapis.com/css?family=Montserrat:700,400);
* {
  box-sizing: border-box;
}
body {
  display: flex;
  justify-content: center;
  align-items: center;
  background: #FFE8A3;
  font-family: 'Montserrat', sans-serif;
}
html, body {
  height: 100%;
}

button {
  border: 5px solid transparent;
  background: #AED6D1;
  color: #55706D;
  border-radius: 40px;
  padding: 15px 30px;
  overflow: hidden;
  width: 200px;
  transition: 
    all        1.2s,
    border     0.5s 1.2s,
    box-shadow 0.3s 1.5s;
  white-space: nowrap;
  text-indent: 23px;
  font-weight: bold;
}
  span {
    display: inline-block;
    transform: translateX(300px);
    font-weight: normal;
    opacity: 0;
    transition: 
      opacity 0.1s 0.5s,
      transform 0.4s 0.5s;
  }
  button:hover {
    text-indent: 0;
    background: #55706D;
    color: #FFE8A3;
    width: 250px;
    border: 10px solid #8DCCC4;
    box-shadow: 3px 3px 2px rgba(black, 0.15);
		}
    span {
      transform: translateX(0);
      opacity: 1;
    }