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

body {
  --size: 15px;
  --color: black;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  color: var(--color);
  background-color: #ff8585;
  background: linear-gradient(
    162deg,
    rgba(255, 133, 133, 1) 0%,
    rgba(227, 84, 95, 1) 100%
  );
}

footer {
  font-size: 0.8em;
}

@media (min-height: 425px) {
  body {
    --size: 25px;
  }

  footer {
    height: 40px;
    font-size: 1em;
  }
}

.container {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  height: 100%;
}

header {
  display: flex;
  justify-content: space-between;
  width: calc(var(--size) * 17);
  font-size: 2em;
  font-weight: 900;
}

.grid {
  display: grid;
  grid-template-columns: repeat(15, auto);
  grid-template-rows: repeat(15, auto);
  border: var(--size) solid var(--color);
}
.tile {
  position: relative;
  width: var(--size);
  height: var(--size);
}
.content {
  position: absolute;
  width: 100%;
  height: 100%;
}

footer {
  margin-top: 20px;
  max-width: calc(var(--size) * 17);
  text-align: center;
}

footer a:visited {
  color: inherit;
}

#youtube,
#youtube-card {
  display: none;
}

@media (min-height: 425px) {
  /** Youtube logo by https://codepen.io/alvaromontoro */
  #youtube {
    z-index: 2;
    display: block;
    width: 100px;
    height: 70px;
    position: absolute;
    bottom: 20px;
    right: 20px;
    background: white;
    border-radius: 50% / 11%;
    transform: scale(0.8);
    transition: transform 0.5s;
  }

  #youtube:hover,
  #youtube:focus {
    transform: scale(0.9);
    background: red;
  }

  #youtube::before {
    content: "";
    display: block;
    position: absolute;
    top: 7.5%;
    left: -6%;
    width: 112%;
    height: 85%;
    background: white;
    border-radius: 9% / 50%;
  }

  #youtube:hover::before,
  #youtube:focus::before {
    background: red;
  }

  #youtube::after {
    content: "";
    display: block;
    position: absolute;
    top: 20px;
    left: 40px;
    width: 45px;
    height: 30px;
    border: 15px solid transparent;
    box-sizing: border-box;
    border-left: 30px solid #ff8585;
  }

  #youtube:hover::after,
  #youtube:focus::after {
    border-left: 30px solid white;
  }

  #youtube span {
    font-size: 0;
    position: absolute;
    width: 0;
    height: 0;
    overflow: hidden;
  }

  #youtube:hover + #youtube-card {
    display: block;
    position: absolute;
    bottom: 12px;
    right: 10px;
    padding: 25px 130px 25px 25px;
    width: 300px;
    background-color: white;
  }
}