在canvas html/css旁边放置按钮

<div style="position: relative;">
  <canvas></canvas>
  <button style="position: absolute; top: 10px; left: 10px;">按钮</button>
</div>

<div>
  <canvas></canvas>
</div>

<script>
  var canvas = document.querySelector('canvas');
  var button = document.createElement('button');
  button.textContent = '按钮';
  button.addEventListener('click', function() {
    // 按钮点击事件处理逻辑
  });
  canvas.parentNode.appendChild(button);
</script>

<div>
  <canvas></canvas>
</div>

<style>
  div::after {
    content: '按钮';
    display: inline-block;
    padding: 5px 10px;
    background-color: #ccc;
    cursor: pointer;
  }
</style>