main.css

*, ::before, ::after {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}

body {
  margin:0;
  padding:0;
  color: white;
  font-family:sans-serif;
}

section.app {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  grid-template-rows: 10.5vh auto 15.75vh;
}

header {
  grid-column: span 12;
}

header:before {
  background-color: yellow;
  width: 65px;
}

footer {
  grid-column: span 12;
}

header, footer {
  background-color: #212121;
  background-image: -webkit-linear-gradient(20deg, #212121 50%, #424242 50%);
}

section.content {
  grid-column: span 12;
}

section.content > section {
  padding-left: 14%;
  padding-right: 14%;
}

section.content > section:before {
  content: 'The quick brown fox jumps over the lazy dog.';
}

section.content > section:first-of-type {
  background-color: #64B5F6;
  background-image: -webkit-linear-gradient(300deg, #64B5F6 50%, #90CAF9 50%);
  min-height: 89.5vh;
  max-height: 89.5vh;
  padding-top: 8%;
  padding-bottom: 8%;
}

section.content > section:nth-of-type(2) {
  background-color: #009688;
  background-image: -webkit-linear-gradient(320deg, #009688 35%, #4DB6AC 35%);
  min-height: 60vh;
  padding-top: 4%;
  padding-bottom: 4%;
}

section.content > section:nth-of-type(3) {
  background-color: #5C6BC0;
  background-image: -webkit-linear-gradient(20deg, #5C6BC0 45%, #3F51B5 45%);
  min-height: 60vh;
  padding-top: 4%;
  padding-bottom: 4%;
}

section.content > section:nth-of-type(4) {
  background-color: #D32F2F;
  background-image: -webkit-linear-gradient(135deg, #D32F2F 45%, #C62828 45%);
  min-height: 70vh;
  padding-top: 6%;
  padding-bottom: 6%;
}