CSS only menu with li in full width and submenu

HTML

<ul>
    <li><a href="#">link</a>
        <ul>
            <li><a href="#">link</a></li>
            <li style="padding-left: 10px;"><a href="#">link</a></li>
            <li style="padding-left: 20px;"><a href="#">link</a></li>
        </ul>
    </li>
    <li><a href="#">link</a>
        <ul>
            <li><a href="#">link</a></li>
            <li style="padding-left: 10px;"><a href="#">link</a></li>
        </ul>
    </li>
    <li><a href="#">link</a>
        <ul>
            <li><a href="#">link</a></li>
            <li style="padding-left: 10px;"><a href="#">link</a></li>
            <li style="padding-left: 20px;"><a href="#">link</a></li>
            <li style="padding-left: 30px;"><a href="#">link</a></li>
        </ul>
    </li>
</ul>

CSS

ul {
    width: 90%;
    margin: 0;
    padding: 0;
    list-style: none;
    display: table;
    table-layout: fixed;
}
ul li {
    display: table-cell;
}
ul li a {
    display: block;
    background: #555;
    color: white;
    height: 40px;
}
    ul li a:hover {
        background: yellow;
        color: black;
    }

/* SUBMENU */
ul li ul {
    display: none;
    position: absolute;
    margin-left: 10px;
}
    ul li ul li {
        display: block;
        width: 171px;
    }
ul li:hover ul {
    display: block;
}

ul li ul li:before {
    content: '';
    position: absolute;
    margin-left: -10px;
	width: 0; 
	height: 0; 
	border-top: 20px solid #555;
	border-left: 5px solid transparent;
	border-right: 5px solid #555;     
	border-bottom: 20px solid transparent;
}
ul li ul li:hover:before {
    content: '';
	border-color: yellow yellow transparent transparent;
}
ul li ul li:after {
    content: '';
    position: absolute;
    margin: -40px 0 0 175px;
    width: 0; 
	height: 0; 
	border-top: 20px solid transparent;
	border-left: 5px solid #555;
	border-right: 5px solid transparent;     
	border-bottom: 20px solid #555;
}
ul li ul li:hover:after {
    content: '';
	border-color: transparent transparent yellow yellow;
}