body{
    margin: 0px;
    text-decoration: none;
}
ul.nav li{
    margin-top: 20px; 
    padding-left: -5px;
    padding-top: -5px;
    text-decoration: none;
}
ul.nav {
    position: absolute;
    overflow: auto;
    margin: 0px;
    margin-top: 80px;
    padding: 0;
}
header {
    background-color: black;
    height: 90px;
    padding: 0px;
    color: white;
    background-color: #3d3d3d;
}
header ul.name {
    background-color: #3d3d3d;
    padding: 0px;
    margin-left: 10px;
}
header h1 {
    margin-top: 20px;
}
hr {
    margin: 0px;
    position: absolute;
    margin-left: 150px;
}

        <header>
            <ul class="name">
                <h1>AutoService</h1>
            </ul>
        </header>
        <nav>
            <ul class="nav">
                <li><h2><a href="#">Каталог<a/><h2></li>
                <li><h2><a href="#">Корзина<a/><h2></li>
                <li><h2><a href="#">Контакты<a/><h2></li>
                <li><h2><a href="#">О нас<a/><h2></li>
            </ul>
        </nav>
        <hr width="1" size="700" class="hr">