<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<style>
html, body {
width: 100%; height: 100%;
margin: 0;
}
body {
display: grid;
grid-template-rows: auto 1fr auto;
}
header {
grid-row: 1;
background: yellowgreen;
}
main {
grid-row: 2;
background: gold;
/*для примера изменение размера*/
overflow: auto;
resize: vertical;
}
footer {
grid-row-end: -1;
background: yellowgreen;
}
</style>
</head>
<body>
<header>header</header>
<main>сontent</main>
<footer>footer</footer>
</body>
</html>