<ul class="parent">
<li class="child"></li>
<li class="child"></li>
<li class="child "></li>
</ul>
* {
box-sizing: border-box;
}
.parent {
list-style-type: none;
display: block;
width: 500px;
position: relative;
padding: 0;
margin: 10px;
height: 150px;
border:1px solid blue;
}
.child {
position: relative;
width: 30%;
height: 100%;
border:1px solid red;
display: block;
float: left;
margin-left: 2.5%;
}