* {

  box-sizing: border-box;

}

.parent > div {

  padding:20px;

}

.parent {

    overflow: hidden;

    position: relative;

    width: 100%;

    color:red;

    background-color:pink;

    min-height:500px;

}

​

.child-left {

   width: 50%;

}

​

.child-right {

    background:green;

    height: 100%;

    position: absolute;

    color:yellow;

    top: 0;

    right: 0;

    width: 50%;

}