You can do this by creating the circle using a pseudo-element and then skewing the container with overflow: hidden
.
The child pseudo-element is reverse skewed to make it appear as though it is not skewed at all.
.shape {
position: relative;
height: 100px;
width: 120px;
overflow: hidden;
-webkit-transform: skew(-45deg);
-moz-transform: skew(-45deg);
transform: skew(-45deg);
}
.shape:after {
position: absolute;
content: '';
top: 0px;
left: 0px;
height: 100px;
width: 100px;
background: black;
border-radius: 50%;
-webkit-transform: skew(45deg);
-moz-transform: skew(45deg);
transform: skew(45deg);
}
<div class="shape"></div>
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