YueWen/node_modules/@dcloudio/uni-components/style/canvas.css

uni-canvas {
  width: 300px;
  height: 150px;
  display: block;
  position: relative;
}

uni-canvas > .uni-canvas-canvas {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}