<div class="close"></div>
.close {
position: relative;
40px;
height: 40px;
}
.close::before,
.close::after {
position: absolute;
content: ' ';
background-color: red;
left: 20px;
1px;
height: 40px;
}
.close::before {
transform: rotate(45deg);
}
.close::after {
transform: rotate(-45deg);
}