#header {
    background: linear-gradient(#000, #000) no-repeat center / 100% 2px;
    display: flex;
    align-items:center;
    gap: 15px;
}

#header > nav {
    background-color: white;
}

#header > nav > ul {
    display: flex;
    gap: 5px;
    list-style-type: none;
    padding: 0;
    margin: 0;
}