htmlcssbordercss-shapesconcave

How do I create concave shaped borders around <div> elements?

I am trying to make concave shaped top and bottom borders around a <div> like this:

Example of what I would like to do

My current CSS:

.div:after {    
    content:'';
    position:absolute;
    left:-600%;
    width:1300%;
    padding-bottom:1300%;
    top:80%;
    background:none;
    border-radius:50%;
    box-shadow: 0px 0px 0px 20px #f2f2f2;
    z-index:-1;
}

But it only works only on the bottom border and sometimes disappears on mobile devices.

Here is JS Fiddle.

Solution

  • You can use :before and :after pseudo elements to draw this shape.

    .div {
  position: relative;
  overflow: hidden;
  padding: 50px 0;
}

.div-inner {
  position: relative;
  background: black;
  height: 120px;
}

.div-inner:before,
.div-inner:after {
  box-shadow: 0 0 0 80px #000;
  border-radius: 100%;
  position: absolute;
  height: 150px;  /* You can change height to increase or decrease concave radius */ 
  content: '';
  right: -20%;
  left: -20%;
  top: 100%;
}

.div-inner:after {
  bottom: 100%;
  top: auto;
}
    <div class="div">
  <div class="div-inner"></div>
</div>