sizer

This is a super-simple component that you can put in a fixed size element allowing it to be resized from the bottom-right.

<div>
  <tosi-sizer></tosi-sizer>
</div>

.preview div {
  position: absolute;
  top: 10px;
  left: 10px;
  width: 200px;
  height: 100px;
  background: #ff02;
  border: 1px solid #555;
}