Creating a custom shape using CSS radial gradient

Question

I am working on a custom shape and am pretty sure I can achieve it using the radial-gradient CSS function. Until now, I have been able to make half of the work, which looks like this :

... using this CSS code :

.block {
    width: 600px;
    height: 200px;
    position: relative;
    margin: 50px auto;
    z-index: 1000;

    background-image: -moz-radial-gradient(
        -23px 50%, /* the -23px left position varies by your "gap" */
        circle closest-corner, /* keep radius to half height */
        transparent 0, /* transparent at center */
        transparent 55px, /*transparent at edge of gap */
        transparent 56px, /* start circle "border" */
        white 57px /* end circle border and begin color of rest of background */
    );
    background-image: -webkit-radial-gradient(-23px 50%, circle closest-side, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, transparent 56px, white 57px);
    background-image: -ms-radial-gradient(-23px 50%, circle closest-corner, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, transparent 56px, white 57px);
    background-image: -o-radial-gradient(-23px 50%, circle closest-corner, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, transparent 56px, white 57px);
    background-image: radial-gradient(-23px 50%, circle closest-corner, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, transparent 56px, white 57px);
}

Now, I'd like to make the same circle shape on the right corner (symmetrical to the circle shape of the left corner). I have tried separating my radial-gradient functions with commas but can't find a way to make it symmetrical to the other one... Can you help?

Thanks!

Answer 1

You can do it like below. 2 backgrounds layer, each one taking half the width (a little bigger than the half to avoid having gap issue)

.box {
  width:400px;
  height:200px;
  margin:20px auto;
  background:
    radial-gradient(circle at left, transparent 50px,white 51px) left,
    radial-gradient(circle at right,transparent 50px,white 51px) right;
  background-size:51% 100%;
  background-repeat:no-repeat;
}

body {
 background:blue;
}

<div class="box">

</div>

Like below if you want to control the origin of the circle:

.box {
  width:400px;
  height:200px;
  margin:20px auto;
  background:
    radial-gradient(circle at -23px             50%,transparent 50px,white 51px) left,
    radial-gradient(circle at calc(100% + 23px) 50%,transparent 50px,white 51px) right;
  background-size:51% 100%;
  background-repeat:no-repeat;
}

body {
 background:blue;
}

<div class="box">

</div>

And with CSS variables for better control and avoid repeating the same code:

.box {
  --rad:transparent 50px,white 51px; /* Gradient*/
  /* Position */
  --x:-23px;  
  --y:50%;
  /**/
  
  width:400px;
  height:200px;
  margin:20px auto;
  background:
    radial-gradient(circle at var(--x)              var(--y),var(--rad)) left,
    radial-gradient(circle at calc(100% - var(--x)) var(--y),var(--rad)) right;
  background-size:51% 100%;
  background-repeat:no-repeat;
}

body {
 background:blue;
}

<div class="box">

</div>

Another syntax without the at for better browser support (safari doesn't support it)

.box {
  --rad:transparent 50px,white 51px; /* Gradient*/
  /* Position */
  --x:-23px;  
  --y:50%;
  /**/
  
  width:400px;
  height:200px;
  margin:20px auto;
  background:
    radial-gradient(circle,var(--rad)) left  calc(150% + var(--x)) top var(--y),
    radial-gradient(circle,var(--rad)) right calc(150% + var(--x)) top var(--y);
  background-size:150% 200%;
  background-repeat:no-repeat;
}

body {
 background:blue;
}

<div class="box">

</div>

Another idea with pseudo element and scale where you need only one gradient:

.box {
  width:400px;
  height:200px;
  margin:20px auto;
  position:relative;
}
.box::before,
.box::after{
  content:"";
  position:absolute;
  top:0;
  left:0;
  bottom:0;
  width:50%;
  background:radial-gradient(circle at -23px 50%,transparent 50px,white 51px);
}
.box::after {
  transform:scaleX(-1);
  transform-origin:right;
}

body {
 background:blue;
}

<div class="box">

</div>