<div class="parent">
<div class="child1"></div>
<div class="child2"></div>
</div>
.parent {
width: 300px;
background-color: pink;
border: 1px solid pink;
}
.child1 {
float: left;
width: 100px;
height: 50px;
background-color: red;
}
.child2 {
float: right;
width: 100px;
height: 50px;
background-color: green;
}