Полоса анимации при загрузке страницы

html, body { 
  margin: 0; 
  padding: 0; 
} 
.box { 
  position: relative; 
  height: 100vh; 
} 
.line { 
  position: absolute; 
  bottom: 0; 
  left: 50%; 
  transform: translateX(-50%); 
  width: 3px; 
  height: 0; 
  background: #000; 
  animation: move 1s; 
  animation-fill-mode: forwards; 
} 
 
@keyframes move { 
  to{ 
    height: 250px; 
  } 
}

<div class="box"> 
 <div class="line"></div>   
</div>