style.css

*{
    padding:0;
    margin:0;
}
ul li{
    display:block;
    float:left;
}
nav{
    width:70vw;
    margin:0 auto;
}
nav:before{
    content:'';
    display:block;
    background:#fff;
    height:10vh;
    width:100%;
    background-color:#000000;
    position:absolute;
    left:0;
    z-index:-1;
}
ul{
    list-style:none;
    height:10vh;
}
ul li a{
    color:#fff;
    display:block;
    height:10vh;
    padding:0 3vh;
}