#elwrap {
  --blur: 2px;
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  position: relative;
}
#elfilter {
  position: absolute;
  z-index: 1;
  -webkit-filter: blur(var(--blur)) contrast(5);
          filter: blur(var(--blur)) contrast(5);
  width: calc(100% + var(--blur) * 2);
  height: calc(100% + var(--blur) * 2);
  top: calc(-1 * var(--blur));
  left: calc(-1 * var(--blur));
}
#elfilter canvas {
  width: 100%;
  height: 100%;
}
body {
  display: grid;
  min-height: 100vh;
  place-content: center;
  padding:0;
  margin:0;
}
canvas {
  display: block;
}