header nav{
    background-color: yellow;
    margin: 0;
}
header nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
    position: relative;
    float: left;
}

header nav ul li {
    display: inline-block;
    background-color: #ddd;
}

header nav a {
    display: block;
    padding: 0 10px;
    font-size: 1em;
    line-height: 40px;
    text-decoration: none; 
    background-color: #222;
    color: white;
}
header nav a:hover{
    background-color: red;
    color: white;
}

.menu {
    display: none;
}

.main {
    background-color: red;
    clear: both;

}
div {
    background-color: white;
}
footer {
    background-color: rgb(255, 0, 0, 0.5);
}

@media all and (max-width: 740px) {
    header nav ul li {
        display: block;
        text-align: center;
    }
    header nav ul {
        width: 100%;
    }
    .menu {
        width: 100%;
        background-color: black;
        color: white;
        display: block;
        text-align: center;
    }
}