如何使用CSS实现外扩弧形边缘的特殊白色背景形状

现有代码问题排查 #

你写的基础逻辑是正确的，缺失了四个角容器的定位、伪元素的背景色和对应偏移属性，补全即可生效。

可选实现方案 #

方案1：多DOM实现（兼容性好） #

需要搭配对应HTML结构：

<div class="concave-box">
  <div id="curved-corner-topleft"></div>
  <div id="curved-corner-topright"></div>
  <div id="curved-corner-bottomleft"></div>
  <div id="curved-corner-bottomright"></div>
  <!-- 写入你的内容 -->
</div>

完整CSS代码：

.concave-box {
  width: 500px;
  height: 300px;
  background: #fff;
  position: relative;
  padding: 24px;
  box-sizing: border-box;
}
#curved-corner-bottomleft,
#curved-corner-bottomright,
#curved-corner-topleft,
#curved-corner-topright {
  width: 24px;
  height: 24px;
  overflow: hidden;
  position: absolute;
}
#curved-corner-topleft {
  top: 0;
  left: 0;
}
#curved-corner-topright {
  top: 0;
  right: 0;
}
#curved-corner-bottomleft {
  bottom: 0;
  left: 0;
}
#curved-corner-bottomright {
  bottom: 0;
  right: 0;
}
#curved-corner-bottomleft:before,
#curved-corner-bottomright:before,
#curved-corner-topleft:before,
#curved-corner-topright:before {
  content: "";
  display: block;
  width: 200%;
  height: 200%;
  position: absolute;
  border-radius: 50%;
  /* 背景色与外层页面背景色保持一致即可 */
  background: #000;
}
#curved-corner-topleft:before {
  transform: translate(-50%, -50%);
}
#curved-corner-topright:before {
  transform: translate(50%, -50%);
}
#curved-corner-bottomleft:before {
  transform: translate(-50%, 50%);
}
#curved-corner-bottomright:before {
  transform: translate(50%, 50%);
}

方案2：径向渐变实现（代码更简洁） #

不需要额外DOM元素，仅用CSS即可实现：

.concave-box {
  width: 500px;
  height: 300px;
  padding: 24px;
  box-sizing: border-box;
  /* 24px为内凹圆角尺寸，#fff为容器背景色，#000为外层页面背景色，可按需调整 */
  background: 
    radial-gradient(circle at top left, transparent 24px, #fff 0) top left,
    radial-gradient(circle at top right, transparent 24px, #fff 0) top right,
    radial-gradient(circle at bottom left, transparent 24px, #fff 0) bottom left,
    radial-gradient(circle at bottom right, transparent 24px, #fff 0) bottom right;
  background-size: 50% 50%;
  background-repeat: no-repeat;
}

注意事项 #

• 方案1兼容低版本IE，适合需要兼容旧浏览器的场景
• 方案2代码量更少，无需额外DOM，支持所有现代浏览器
• 两种方案的内凹尺寸、背景色都可以根据你的实际需求调整

内容的提问来源于stack exchange，提问作者ololo