Submenu below slider in Wordpress

I'm using WordPress (with Antreas theme).

I created a sub menu for it, but the slider is above the sub-menu.

When I set z-index on slider (below the slider): the sub menu is working, but the controls on the slider are not.

How can I fix it?

Thanks advanced

My Website

Code: Source Code

.slider {
    padding: 0;
    margin: 0;
    position: relative;
    text-align: center;
    transition: 0.3s all;
    background-color: #333333;
    z-index: -1 !important;
}

.menu-main li ul {
    position: absolute;
    margin: 5px 0 0;
    background-color: #fff;
    border: 1px solid #eee;
    transition-delay: 0.2s;
    visibility: hidden;
    opacity: 0;
    top: 100%;
    left: 0;
    z-index: 9998 !important;
    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.07);
}

.sub-menu {
    color: #000 !important;
    background-color: #ccc;
}