CSS: position: relative absolute

<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;
}