/* https://alvarotrigo.com/blog/animated-backgrounds-css#19)-retro-grid-animated-css-background */

html,
body {
  margin: 0;
  height: 100%;
}

/* ............................................................... */
/* ............................................................... */
/* ............................................................... */
#retrobg {
  position: relative;
  overflow: hidden;
  height: 100%;
  color: #a3c;
  background-color: #000;
}

/* ............................................................... */
#retrobg-sky {
  position: absolute;
  display: flex;
  align-items: flex-end;
  justify-content: center;
  top: 0;
  width: 100%;
  height: 55%;
  background: linear-gradient( #214 75%, #249 );
}

/* ............................................................... */
#retrobg-sunWrap {
  position: relative;
  width: 40%;
  margin-bottom: -15%;
}
#retrobg-sun {
  --glow-color: #d44;
  padding-top: 100%;
  border-radius: 50%;
  background-image: linear-gradient( #fcdf11, #ff623f, #fe2085 50% );
  box-shadow: 0 0 160px 80px var( --glow-color );
  animation: 2s ease infinite alternate retrobg-sun-glow-anim;
}
.retrobg-shutdown #retrobg-sun {
  background-image: linear-gradient( #000, #000 40% );
  --glow-color: #000;
}
@keyframes retrobg-sun-glow-anim {
  from { box-shadow: 0 0 160px 80px var( --glow-color ); }
  to   { box-shadow: 0 0 200px 95px var( --glow-color ); }
}

/* ............................................................... */
#retrobg-stars {
  position: absolute;
  width: 100%;
  height: 100%;
}
.retrobg-star {
  position: absolute;
  border-radius: 50%;
  width: 2px;
  height: 2px;
  background-color: #fff;
}

/* ............................................................... */
#retrobg-mountains {
  position: absolute;
  width: 100%;
  height: 30%;
}
.retrobg-mountain {
  position: absolute;
  width: 30%;
  height: 100%;
  background-image: linear-gradient( #000 70%, #111 85%, #fff1 );
}
#retrobg-mountains-left { left: 0; clip-path: polygon( 0% 100%,0% 55%,5% 60%,10% 55%,20% 50%,25% 42%,30% 38%,33% 35%,40% 45%,50% 50%,60% 70%,70% 85%,75% 82%,80% 91%,85% 90%,90% 95%,95% 98%,100% 100% ); }
#retrobg-mountains-right { right: 0; clip-path: polygon( 0% 100%,5% 95%,10% 85%,15% 87%,20% 80%,25% 78%,30% 65%,40% 70%,50% 57%,60% 53%,67% 68%,70% 70%,75% 66%,80% 55%,90% 50%,95% 60%,100% 57%,100% 100% ); }

/* ............................................................... */
#retrobg-cityWrap {
  position: absolute;
  width: 50%;
  margin-left: -1%;
}
#retrobg-city {
  padding-top: 20%;
}
.retrobg-building {
  position: absolute;
  width: 5%;
  height: 100%;
  bottom: 0;
  border-radius: 4px 4px 0 0;
  background-image: linear-gradient( 0deg, rgba( 17, 17, 34, 0 ), #112 30px, #000 );
}
.retrobg-building:nth-child( odd ) {
  background-image: linear-gradient( 0deg, rgba( 24, 24, 42, 0 ), #223 30px, #000 );
}
.retrobg-antenna::after {
  content: "";
  position: absolute;
  left: 50%;
  margin-left: calc( -1px - 5% );
  bottom: 100%;
  width: 10%;
  min-width: 2px;
  height: 33%;
  background-color: #000;
}

/* ............................................................... */
#retrobg-ground {
  position: absolute;
  overflow: hidden;
  width: 100%;
  height: 45%;
  bottom: 0;
  border-top: 2px solid #bf578c;
  background-color: #000;
}
.retrobg-shutdown #retrobg-ground {
  border-color: #000;
}
#retrobg-groundShadow {
  position: absolute;
  top: 0;
  width: 100%;
  height: 100%;
  background-image: linear-gradient( #000 0%, transparent );
}

/* ............................................................... */
#retrobg-linesWrap {
  height: 100%;
  perspective: 1000px;
  perspective-origin: center top;
}
#retrobg-lines {
  position: absolute;
  width: 100%;
  height: 100%;
  transform-origin: top center;
  animation: .35s linear infinite retrobg-lines-anim;
}
.retrobg-shutdown #retrobg-lines {
  animation-duration: 5s;
}
@keyframes retrobg-lines-anim {
  from { transform: rotateX( 84deg ) translateY( 0 ); }
  to { transform: rotateX( 84deg ) translateY( 100px ); }
}
#retrobg-hlines,
#retrobg-vlines {
  position: absolute;
  left: calc( ( 900% - 100% ) / -2 );
  width: 900%;
  height: 500%;
}
#retrobg-vlines {
  display: flex;
  justify-content: center;
}
.retrobg-hline,
.retrobg-vline {
  width: 100%;
  height: 100%;
  background-color: currentColor;
}
.retrobg-hline { height: 3px; }
.retrobg-vline { width: 3px; }
.retrobg-hline + .retrobg-hline { margin-top: 98px; }
.retrobg-vline + .retrobg-vline { margin-left: 48px; }