I want to put one element under another element. I am using position: absolute in CSS.

.first{
    width:70%;
    height:300px;
    position:absolute;
    border:1px solid red;
 }
.second{
    border:2px solid blue;
    width:40%;
    height:200px;
}

I want the blue box to be positioned under the red box. How could I achieve this?