html - CSS drop down menu hover effect

Question

i was trying to make a simple css drop down menu. I'm not able to achieve the drop down sub menu when you hover over a link. Below is my html and css rule, thanks.

    ul#menu li
    {
        position:relative;
        list-style-type:none;
        float: left;
        padding:0px;
        width: 125px;
        height: 25px;
    }
    ul#sub1 li
    {
        position:absolute;
        left:0;
        width:125px;
        visibility: hidden;
    }
    ul#menu li:hover #sub1
    {
        visibility:visible;
    }


    <ul id="menu">
        <li><a href="#">Hyperlink 1</a></li>
        <li><a href="#">Hyperlink 2</a>
            <ul id="sub1"> 
                <li><a href="#">Hyperlink 2.1</a></li>
                <li><a href="#">Hyperlink 2.2</a></li>
            </ul>
        </li>
        <li><a href="#">Hyperlink 3</a></li>
        <li><a href="#">Hyperlink 4</a></li>
    </ul>

Answer 1

Try this:

ul#sub1 {
    position:absolute;
    left:0;
    width:125px;
    visibility: hidden;
}
ul#menu li:hover #sub1 {
    visibility:visible;
}

Fiddle

issue is that your your menu ul is visible (always) but the li's inside them are invisible (always) due to the selector of the this rule ul#sub1 li.

Do remember that visibility:hidden hides the element but still occupies space in DOM, whereas display:none hides the element and takes it out of page element flow

Also you necessarily do not need to use ids in css selectors especially for a menu like this. You can achieve it without that, consider the situation with many level menus, by using ids you will have to write selectors indefinitely. Instead you can try something like this.

ul#menu ul {
    padding:0px;
}
ul#menu li {
    position:relative;
    list-style-type:none;
    float: left;
    width: 125px;
}
ul#menu li > ul {
    display: none;
}
ul#menu li:hover > ul {
    display:block;
}

Fiddle