<link href='https://fonts.googleapis.com/css?family=Roboto:400,700' rel='stylesheet' type='text/css'>
 <div class="parent">
		  Parent
		  <div class="child">Child</div>
	</div>
*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html{
    font: normal 20px 'Roboto', sans-serif;
    text-align: center;
}


.parent{
    width: 400px;

    height: 400px;
    background-color: #a4dd3c;
    padding-top: 40px;
}

.child{
    width: 100vw;

    height: 150px;
    margin-top: 10px;
    padding-top: 20px;
    background-color: #8280ff;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.