<!DOCTYPE html>
<html>

<head>
</head>

<body>
  <style>
    :root {
      margin: 0px;
      scroll-start: 100px;
    }

    #spacer {
      height: 100vh;
      width: 100vw;
    }

    #scroll_start_target {
      width: 100px;
      height: 100px;
      background-color: blue;
    }

    #anchor_target {
      width: 100px;
      height: 100px;
      background-color: red;
    }
  </style>
  <a id="anchor_target_link" href="#anchor_target"></a>
  <div id="spacer"></div>
  <div id="scroll_start_target"></div>
  <div id="anchor_target">
  </div>
</body>

</html>