How to add ul class on nav

I’ve been learning to convert HTML to WordPress and want to convert on to class like this:

<div class="mainmenu pull-left">
    <ul class="nav navbar-nav collapse navbar-collapse">
        <li><a href="https://wordpress.stackexchange.com/questions/191299/index.html" class="active">Home</a></li>
        <li class="dropdown"><a href="#">Shop<i class="fa fa-angle-down"></i></a>
            <ul role="menu" class="sub-menu">
                <li><a href="shop.html">Products</a></li>
                <li><a href="product-details.html">Product Details</a></li> 
                <li><a href="checkout.html">Checkout</a></li> 
                <li><a href="cart.html">Cart</a></li> 
                <li><a href="login.html">Login</a></li> 
            </ul>
        </li> 
        <li class="dropdown"><a href="#">Blog<i class="fa fa-angle-down"></i></a>
            <ul role="menu" class="sub-menu">
                <li><a href="blog.html">Blog List</a></li>
                <li><a href="blog-single.html">Blog Single</a></li>
            </ul>
        </li> 
        <li><a href="404.html">404</a></li>
        <li><a href="contact-us.html">Contact</a></li>
    </ul>
</div>

This what I’ve done:

if ( ! function_exists( 'mytheme_setup' ) ) :
    function wpflex_setup() {  
        register_nav_menus( array(
            'primary' => 'Primary Menu'
        ) );
    }
endif;

wp_nav_menu( array( 
    'theme_location' => 'top-menu',
    'container'      => '',
    'menu_class'     => 'mainmenu pull-left',
) );

How to add class for ul?

It’s simple just you need to add items_wrap parameter and add or edit class attr:

wp_nav_menu( array(
    'theme_location' => 'top-menu',
    'container' => false,
    'items_wrap' => '<ul class="nav your_custom_class">%3$s</ul>',
));