single element hamburger

.htm

<style>
.hamburger {
  box-sizing: border-box;
  width: 25px;
  height: 20px;
  border-top: 2px solid;
  border-bottom: 2px solid;
  position: relative;
}
.hamburger::before{
  content: "";
  position: absolute;
  width: 100%;
  top: calc(50% - 1px);
  height: 2px;
  background: currentColor;
}
</style>
<div class="hamburger"></div>