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

Question

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

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 .

Answer 1

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>