chromium/chrome/browser/resources/lens/overlay/region_selection.html

<style>
  #highlightImgContainer {
    display: none;
  }

  #regionSelectionCanvas {
    top: 0;
    left: 0;
    position: absolute;
  }
</style>
<canvas id="regionSelectionCanvas" height="[[canvasPhysicalHeight]]"
  width="[[canvasPhysicalWidth]]"
  style$="height: [[canvasHeight]]px; width: [[canvasWidth]]px;"></canvas>
<!-- Provides image source for canvas; element is not displayed. -->
<div id="highlightImgContainer">
  <canvas id="highlightImgCanvas">
</div>