<div class="box one">1</div>
<div class="box two">2</div>
<div class="box three">3</div>
<div class="box four">4</div>
.box {
  display:inline-grid;
  place-content:center;
  font-size:35px;
  font-weight:bold;
  width:200px;
  aspect-ratio:1;
  border:1px solid ;
}
.one {
  background:
    radial-gradient(20px at 25% 50% ,blue 99%,#0000 101%) bottom/80px 40px no-repeat,
    radial-gradient(20px at 75% 100%,#0000 98%,red) 50% calc(100% - 20px)/80px 100% no-repeat;
}
.two {
  background:
    radial-gradient(20px at 25% 50% ,blue 99%,#0000 101%) bottom/80px 40px repeat-x,
    radial-gradient(20px at 75% 100%,#0000 98%,red) 50% calc(100% - 20px)/80px 100% repeat-x;
}
.three {
  background:
    radial-gradient(20px at 75% 100%,#0000 98%,red) 50% calc(100% - 20px)/80px 100% repeat-x,
    radial-gradient(20px at 25% 50% ,red 99%,#0000 101%) bottom/80px 40px repeat-x;
}
.four {
  border:none;
  background:linear-gradient(135deg,#1f005c, #5b0060, #870160, #ac255e, #ca485c, #e16b5c, #f39060, #ffb56b);
  --mask: 
    radial-gradient(20px at 75% 100%,#0000 98%,#000) 50% calc(100% - 20px)/80px 100% repeat-x,
    radial-gradient(20px at 25% 50% ,#000 99%,#0000 101%) bottom/80px 40px repeat-x;
-webkit-mask: var(--mask);
        mask: var(--mask);
}

body {
  background: linear-gradient(90deg,#ddd,#fff);
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.