<div class="ruled-paper" role="main">
  <div class="ruled-paper-header"></div>
  <div class="ruled-paper-body" contenteditable="true">Hello, world!</div>
</div>

:root {
  --bg-color: #fff;
  --margin-line-color: #ec7063;
  --ruling-line-color: #85c1e9;
}

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

body {
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  padding: 0;
  margin: 0;
}

.ruled-paper {
  width: 100%;
  height: 100%;
  background-color: var(--bg-color);
  display: flex;
  flex-direction: column;
}

.ruled-paper .ruled-paper-header {
  background-image: linear-gradient(90deg, transparent 79px, var(--margin-line-color) 79px, var(--margin-line-color) 81px, transparent 81px);
  background-size: 100% 1.2em;
  flex-grow: 1;
}

.ruled-paper .ruled-paper-body {
  background-image: linear-gradient(90deg, transparent 79px, var(--margin-line-color) 79px, var(--margin-line-color) 81px, transparent 81px), linear-gradient(var(--ruling-line-color) .1em, transparent .1em);
  background-size: 100% 1.2em;
  flex-grow: 8;
  padding-top: .2rem;
  padding-left: 6rem;
  line-height: 1.2;
}