*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body{
    text-align: center;
    font-size: 2em;
}

#webpage:target, #pop-up:target{
    display: block;
}

.webpage{
    position: absolute;
    width: 100%;
    z-index: 1;
}

header{
    height: 15vh;
    background-color: red;
}

main{
    height: 70vh;
    background-color: green;
}

footer{
    height: 15vh;
    background-color: blue;
}

.pop-up{
    position: absolute;
    z-index: 2;
    background: rgba(0, 0, 0, 0.8);
    color: #fff;
    width: 100%;
    height: 100vh;
    display: none;
    padding: 50px;
}

#webpage a{
    text-decoration: none;
    color: #000;
}

#pop-up a{
    text-decoration: none;
    color: #fff;
}