<!DOCTYPE html>
<div style="display: flex; width: 100px; border: solid; align-items: baseline;">
  <div style="width: 50px; height: 50px;">
    <div style="width: 50px; height: 50px; position: relative; overflow: auto;">
      <canvas width=10 height=10 style="width: 80%; background: green;"></canvas>
      <div id="target" style="position: absolute; width: 10px; height: 10px; background: red; top: 100px;"></div>
    </div>
  </div>
  <div style="width: 50px; height: 50px; background: green;"></div>
</div>