<p>1</p>
<p>2</p>

body {
  padding: 0;
  margin: 0;
}
#one {
  background: red;
  height: 100vh;
  overflow: hidden;
}
#two {
  height: 100%;
  background: #ccc;
  display: flex;
  flex-direction: column;
  justify-content: center;
}