* {
  box-sizing: border-box;
}

body {
  height: 100vh;
  margin: 0;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.background {
  background: url("https://images.wallpaperscraft.com/image/mountain_river_snow_nature_92721_1920x1080.jpg")
    no-repeat center center/cover;
  position: absolute;
  top: -20px;
  right: -20px;
  bottom: -20px;
  left: -20px;
  z-index: -1;
  filter: blur(20px);
}