边界半径

您可以在右侧添加相同的样式border-radius，占据剩下的30％.

Border-Radius

You could just add the same style border-radius to the right, taking up the other 30% you have left over.

body {
  background: lightblue;
}
#box {
  width: 500px;
  height: auto;
  border-bottom: 3px solid green;
  -moz-border-radius-bottomleft: 70% 40px;
  -webkit-border-bottom-left-radius: 70% 40px;
  -moz-border-radius-bottomright: 30% 20px;
  -webkit-border-bottom-right-radius: 30% 20px;
  -webkit-box-shadow: 0 3px 7px 0 rgba(0, 0, 0, 0.91);
  box-shadow: 0 3px 7px 0 rgba(0, 0, 0, 0.91);
}

<img id="box" src="http://www.hdwallpapersinn.com/wp-content/uploads/2014/11/Sunset-Cityscape-Scene.jpg" />

您也可以考虑使用clip-path来获取所需的区域.可悲的是，这不允许box-shadows

You could also look into using a clip-path to get the area you want. Sadly, this doesn't allow for box-shadows

body {
  background: lightblue;
}
.container {
  -webkit-clip-path: ellipse(100% 56% at 71% 39%);
  clip-path: ellipse(100% 56% at 71% 39%);
  width: 500px;
  height: auto;
  background: green;
}
img {
  -webkit-clip-path: ellipse(100% 56% at 71% 39%);
  clip-path: ellipse(100% 56% at 71% 39%);
  width: 500px;
  height: auto;
}

<div class="container">
  <img src="http://www.hdwallpapersinn.com/wp-content/uploads/2014/11/Sunset-Cityscape-Scene.jpg" />
</div>

剪切路径支持

您还可以使用SVG获得所需的形状.

You can also achieve the shape required with an SVG.

body {
  background: lightblue;
}

<svg width="500" height="250" viewBox="0 0 100 50">
  <defs>
    <pattern id="image" patternUnits="userSpaceOnUse" height="50" width="100">
      <image x="0" y="0" height="50" width="100" xlink:href="https://31.media.tumblr.com/cd4319a4a4ba642649bcf7936d48eec8/tumblr_inline_mn089qqjI71qz4rgp.png"></image>
    </pattern>
    <filter id="blur" x="0" y="0" width="100%" height="110%">
      <feOffset result="offOut" in="SourceAlpha" dx="0" dy="1" />
      <feGaussianBlur result="blurOut" in="offOut" stdDeviation="2" />
      <feBlend in="SourceGraphic" in2="blurOut" mode="normal" />
    </filter>
  </defs>
  <g class="curve">
    <path fill="url(#image)" filter="url(#blur)" stroke="green" stroke-width="1" d="M-1,-1 
             L-1,40 
             C-1,40 60,45 101,42 
             L101,-1z" />
  </g>
</svg>

body {
  background: lightblue;
  margin: 0;
  padding: 0;
}

<svg width="100%" viewBox="0 0 100 50" preserveAspectRatio="none" height="150px">
  <defs>
    <filter id="blur" x="0" y="0" width="100%" height="110%">
      <feOffset result="offOut" in="SourceAlpha" dx="0" dy="1" />
      <feGaussianBlur result="blurOut" in="offOut" stdDeviation="2" />
      <feBlend in="SourceGraphic" in2="blurOut" mode="normal" />
    </filter>
  </defs>
  <path fill="#ffffff" filter="url(#blur)" stroke="green" stroke-width="1" d="M-1,-1 
             L-1,40 
             C-1,40 60,45 101,42 
             L101,-1z" />
</svg>