Code Playground

@charset "UTF-8";
@import url(https://fonts.googleapis.com/css?family=Nunito+Sans:300,400,600,700,800);
*,
:after,
:before {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}
@import url("https://fonts.googleapis.com/css2?family=Montserrat:wght@500&display=swap");
:root {
  --x: 50vw;
  --y: 43vh;
  --size: max(70vmin, 250px);
  --blur: 0.5vmax;
}
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
html,
body {
  background-color: black;
  overscroll-behavior-x: none;
  overscroll-behavior-y: none;
  overflow: hidden;
  /*
  cursor: none;
  */
  user-select: none;
}
body {
  pisition: relative;
  width: 100vw;
  height: 100vh;
  font-family: "Montserrat", serif;
  text-align: center;
  line-height: 1;
  color: #333;
  display: flex;
  justify-content: center;
  align-items: center;
}
main {
  pisition: relative;
  color: crimson;
  mix-blend-mode: color-burn;
  z-index: 0;
}
h1 {
  font-size: max(18vmin, 50px);
}
h2 {
  margin-top: 0.2em;
  font-size: max(10vmin, 40px);
}
#bg {
  /*
  filter: brightness(0.8) blur(0.5vmax);
*/
  filter: blur(var(--blur));
}
#bg,
#bg_mask {
  /* ふちボケ対策 */
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  margin: calc(var(--blur) * -1);

background-image: url(https://images.unsplash.com/photo-1532153955177-f59af40d6472?crop=entropy&cs=srgb&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE2OTg2NTgxNzR8&ixlib=rb-4.0.3&q=100&w=2000);
  background-size: cover;
  background-repeat: no-repeat;
  background-position: center;
  z-index: 0;
}
#spotlight,
#bg_mask {
  background-color: rgba(0, 0, 0, 0.6);
  mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='546.133' height='448' viewBox='-20 -20 552 460'%3E%3Cdefs%3E%3Cfilter id='filter'%3E%3CfeGaussianBlur stdDeviation='10' /%3E%3C/filter%3E%3C/defs%3E%3Cpath fill='black' filter='url(%23filter)' d='M257 112c.28-12.93 5.99-29.47 11.75-41C300.62 7.27 376.04-17.2 440 12.31c33.67 15.54 60.35 48.63 68.77 84.69 4.11 17.63 3.43 29.19 3.23 47-.23 19.09-8.22 50.95-14.95 69C468.4 289.85 404.82 349.11 333 386.26L278 412c-4.6 1.84-17.87 7.79-22 7.79-4.18 0-20.12-7.02-25-8.99-21.1-8.51-41.08-18.56-61-29.5C95.65 340.48 30.02 274.83 7.88 191 .49 162.99-.33 146.56 0 118c.17-14.32 6.36-34.21 12.75-47C19.82 56.86 29.21 43.78 41 33.17c49.22-44.3 123.25-44.16 173-.88 10.52 9.15 20.7 22.36 27.22 34.71 6.75 12.8 13.46 30.42 13.78 45h2Z'/%3E%3C/svg%3E"),
    linear-gradient(#fff 0 0);
  mask-size: var(--size), 100%;
  mask-position: calc(var(--x) - var(--size) / 2)
      calc(var(--y) - var(--size) / 2 * 0.65),
    left top;
  mask-repeat: no-repeat;
  mask-mode: alpha;
}
#spotlight {
  position: fixed;
  top: 0;
  left: 0;
  height: 100vh;
  width: 100vw;

-webkit-mask-composite: destination-out;
  mask-composite: exclude;
  z-index: 1;
}
#bg_mask {
  mask-size: var(--size), 0;
}

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