<div class="icon"></div>
.icon {
font-size: 100px;
border: 0.1em solid black;
border-radius: 50%;
display: inline-block;
width: 1em;
height: 1em;
position: relative;
transform: rotate(45deg);
}
.icon::before {
content: "";
display: inline-block;
position: absolute;
background: black;
width: 0.1em;
height: 100%;
left: 0.5em;
transform: translateX(-50%);
}