<img src="https://picsum.photos/id/195/300/300" alt="walking in a city" >
<img src="https://picsum.photos/id/216/300/300" alt="walking in a forest" style="background-image: linear-gradient(45deg in oklch,#4ECDC4,#FF6B6B);">

img {
  --s: 20px;  /* control the size of the wave */
  --w: 300px; /* preferred image width */
  
  width: round(var(--w),4*var(--s)); 
  aspect-ratio: 1;
  padding: var(--s);
  border: var(--s) solid #0000;
  box-sizing: border-box;
  background: conic-gradient(#FF4E50,#5E9FA3,#FF4E50) border-box;
  border-radius: calc(3.5*var(--s)); 
  mask: 
    radial-gradient(calc(sqrt(2)*var(--s)),#000 calc(100% - 1px),#0000),
    conic-gradient(#000 0 0) content-box,
    radial-gradient(calc(sqrt(2)*var(--s)),#0000 100%,#000 calc(100% + 1px)) 
     var(--s) var(--s) padding-box;
  mask-size: calc(var(--s)*4) calc(var(--s)*4);
}


body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  grid-auto-flow: column;
  place-content: center;
  gap: 40px;
  background: #F2E9E1;
}