Creating a custom shape using CSS radial gradient - css

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>