<div class="course-b">
<div class="outer">
<div class="inner"></div>
</div>
</div>
.outer{
margin: 50px;
width: 200px;
height: 200px;
background: gray;
position: relative;
}
.inner{
bottom: 0;
left: -20px;
width: 240px;
height: 10px;
position: absolute;
background: black;
}