header {
    position: fixed;
    top: 0px;
    width: 100%;
    text-align: center;
    padding-top: 10px;
    background: var(--fullblock);
}

nav ul {
    list-style-type: none;
    padding: 0;
    display: inline-block;
    margin: 0;
}

nav li {
    float: left;
    text-align: center;
    
}

nav li a {
    display: block;
    width: 100px;
    height: 30px;
    border: 1px solid #4d4d4d;
    background-color: #4d4d4d;
    color: white;
    text-decoration: none;
    margin: 5px;
    text-align: center;
    line-height: 30px;
}

nav li a:hover {
    background-color: orange;
}