body {
    margin:0;
    padding:0;
    width:100%;
    min-height:115vh;
    display: grid;
    grid-template-rows: 5vh minmax(95vh, max-content) 15vh;
}

body > header {
    background-color: red;
}

body > main {
    background-color: blue;
}

body > footer {
    background-color: green;
}