practice.css

*
{
     margin:0;
     padding:0;
}

header
{
    background-image:-moz-linear-gradient(rgba) url(jumia.jpg);
    height: 90vh;
    background-size: cover;
    background-position: center;
}

.main-nav
{
    float:right;
    list-style:none;
    margin-top:30px;
}

.main-nav li
{
    display: inline-block;
}

.main-nav li a
{
    color:white;
    text-decoration:none;
    padding: 5px 20px;
    font-family:"Roboto",sans-serif;
    font-size:15px
}