<header class="header"><h1>Header</h2>
<nav>Nav stuff or whatever</nav>
</header>
<main class="main">
  <h2>Scrollable section</h2>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
      <p>Content to scroll</p>
</main>
<footer>Footer</footer>

html {
  box-sizing: border-box;
  background: #666;
}
*,
*:before,
*:after {
  box-sizing: inherit;
}
html,
body {
  margin: 0;
  padding: 0;
}
body {
  display: flex;
  min-height: 100vh;
  flex-direction: column;
  max-width: 1280px;
  margin: auto;
}
.main {
  flex: 1;
  background: #ccc;
  padding: 10px;
}
header,
footer,
nav {
  background: green;
}
header {
  position: sticky;
  top: 0;
}
footer {
  position: sticky;
  bottom: 0;
  padding: 10px;
}
h1,
nav {
  padding: 10px;
}

nav {
  background: red;
}