Arrow in pure css

<div class="arrow"></div>

.arrow {
  --thickness: 8px;
  --length: 10px;
  
  display: inline-block;
  padding: var(--length);
  border: solid black;
  border-width: 0 var(--thickness) var(--thickness) 0;
  
  transform: rotate(-45deg);
  -webkit-transform: rotate(-45deg);
}