[css] Draw a curve with css

You could use an asymmetrical border to make curves with CSS.

border-radius: 50%/100px 100px 0 0;

VIEW DEMO

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.box {_x000D_
  width: 500px; _x000D_
  height: 100px;  _x000D_
  border: solid 5px #000;_x000D_
  border-color: #000 transparent transparent transparent;_x000D_
  border-radius: 50%/100px 100px 0 0;_x000D_
}
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<div class="box"></div>
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