body {
    margin: 0;
}
ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
    width: 100%;
    position: fixed;
    top: 0;
}  
li {
    float: left;
    display: block;
    color: #fff;
    font-size: 18px;
    text-align: center;
    padding: 10px 20px;
}
p {
    margin: 25px 100px;
}