1px

Question

https://codesandbox.io/s/frosty-haze-r4v9r

我正在使用伪类将默认的单选输入替换为自定义的单选输入，并试图准确了解其工作原理。

为什么检查时我的：before元素上的高度和宽度1px不能显示，但是2px的值可以正确显示？

HTML和CSS渲染

.css-19erv9f {
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  cursor: pointer;
}
.css-19erv9f:before {
  content: "";
  position: absolute;
  z-index: 1;
  top: 0;
  left: 0;
  width: 1px;
  height: 1px;
  background: blue;
  -webkit-transform: scale(0, 0);
  -ms-transform: scale(0, 0);
  transform: scale(0, 0);
}
.css-19erv9f:checked:before {
  -webkit-transform: scale(1);
  -ms-transform: scale(1);
  transform: scale(1);
}
.css-19erv9f:focus {
  outline: none;
}
.css-19erv9f:after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 15px;
  height: 15px;
  border: 1px solid pink;
}

<div id="root">
  <div class="App"><input type="radio" class="css-19erv9f"></div>
</div>