body {
  margin: 50px;
  font-family: Arial, sans-serif;
  background: #1d1d1d;
  color: #eee;
}

video {
  width: 600px;
}

a:link,
a:active,
a:visited {
  color: #f60;
}

:root {
  --grid-color: #777;
  --grid-width: 50px;
  --grid-height: 50px;
  --grid-thickness: 1px;
}

.spacer {
  border-left: 1px solid #777;
  border-right: 1px solid #777;
  height: 80vh;
  width: 600px;
  background: #000;
  margin: 0;
  padding: 0;
  background: #111;
  background-image: linear-gradient(
    var(--grid-color) var(--grid-thickness),
    transparent var(--grid-thickness)
  );
  background-size: var(--grid-width) var(--grid-height);
}

@media only screen and (max-width: 700px) {
  /* For mobile phones: */
  video,
  .spacer {
    width: 100%;
  }

  body {
    font-size: 0.8em;
  }
}