Untitled

<div class="container">

  <div>First</div>

  <div>Second Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus porta elit vel ante hendrerit facilisis. Curabitur aliquam sollicitudin diam, id posuere elit consectetur nec. Vestibulum quam dolor, feugiat in posuere a, posuere imperdiet tellus. Mauris sed ligula vitae urna consequat aliquet. Curabitur pellentesque consectetur ornare. Pellentesque vel euismod odio. Nulla tempus pharetra nulla. In justo dolor, sollicitudin nec commodo sit amet, adipiscing eget lectus.</div>

</div>

.container {

  display: table; /* optional */

  width: 100%; /* optional */

}

.container div {

  display: table-cell;

}

.container div:first-child {

  background: yellow;

}

.container div:last-child {

  background: #CCC;

}