Width: 50%; height: 300px

.contener{

width: 50%;
height: 300px;
margin: auto;
margin-top: 50px;
}
.contener .left{

width: 50%;

height: 300px;
display: inline-block;

}.contener .left .box1{

background-color: yellowgreen;
width: 99%;
height: 145px;
margin-bottom: 10px;
}
.contener .left .box2{
background-color: crimson;
width: 99%;
height: 145px;
}
.contener .right{
display: inline-block;
background-color: blue;
width: 49%;
height: 300px;
}

DOCTYPE html>