Użyj @keyframes
<div>
<div id="box" class="box">
kwadrat
</div>
</div>
.box {
width: 100px;
height: 100px;
background-color: blue;
color: #fff;
font-weight: 700;
font-size: 1.2em;
text-align: center;
line-height: 100px;
position: absolute;
}
.slideSlant{
animation: slideSlant .5s forwards;
}
@keyframes slideSlant {
from {
top: 0;
left: 0;
}
to {
top: 100px;
left: 100px;
}
}
const el = document.getElementById('box');
el.classList.add("slideSlant");