<div class='wrap'>
  <div class='box'></div>
</div>
.wrap {
  height: 100px;
  width: 100px;
  padding: 1px;
  background: linear-gradient(to right, red, orange);

  > .box {
    height: 100%;
    width: 100%;
    background: white;
  }
}

html {
  background: lightgray;
}
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