css hover affect unrelated element

Question

I'm trying to show a relevant submenu when the user hovers over an item in the main menu. The problem I am having is that I need to have a common parent for the hover selector to do its magic, but then that seems to screw up my styling. Any suggestions that forgo javascript/jquery would be appreciated as I use that as a crutch too much for things that I should probably be solving with css alone.

HTML

<div id="header">
    <div id="header_headline">
        Heading
    </div>
    <div id="menu">
        <div id="menu_inset">
            <a href="#" class="menu_item" id="menu_item_home">HOME</a>
            <a href="#" class="menu_item" id="menu_item_profile">PROFILE<div class="sub_menu_arrow"></div></a>
            <a href="#" class="menu_item" id="menu_item_projects">PROJECTS<div class="sub_menu_arrow"></div></a>
            <a href="#" class="menu_item" id="menu_item_news">NEWS</a>
            <a href="#" class="menu_item" id="menu_item_contacts">CONTACT</a>
        </div>
    </div>
    <div id="sub_menu">
        <div class="sub_menu_inset" id="sub_menu_profile">
            <a href="#">1</a>
            <a href="#">2</a>
            <a href="#">3</a>               
        </div>
        <div class="sub_menu_inset" id="sub_menu_projects">
            <a href="#">1</a>
            <a href="#">2</a>
            <a href="#">3</a>               
            <a href="#">4</a>               
        </div>
    </div>
</div>

CSS:

html, body {
    width: 100%;
    height: 100%;
    border: 0;
    padding: 0;
    margin: 0;
    font-family: 'Pathway Gothic One', sans-serif;
    color: #212121;
}

a {
    text-decoration: none;
    color: #212121;
}

#header {
    width: 100%;
}

#header_headline {
    margin: 1em 1em 1em 1em;
    font-size: 2em;
    text-transform: uppercase;
}

#menu {
    margin-top: 1em;
    width: 100%;
    text-align: center;
    white-space: nowrap;
}

#menu_inset {
    display: inline-block;
    word-spacing: 5em;
}

.menu_item {
    position: relative;
}

.menu_item:hover .sub_menu_arrow {
    display: inline-block;
}

#menu_item_profile:hover ~ #sub_menu_profile {
    display: inline-block;
}

#menu_item_people:hover ~ #sub_menu_people {
    display: inline-block;
}

.sub_menu_arrow {
    position: absolute;
    display: none;
    left: 0;
    width: 100%;
    bottom: -1.05em;
}
.sub_menu_arrow:after {
    content: '';
    margin: 0 auto;
    border-width: 0 .5em .5em;
    border-style: solid;
    border-color: #CCCCCC transparent;
    display: block;
    width: 0;
}

#sub_menu {
    margin-top: 1em;
    background-color: #CCCCCC;
    width: 100%;
    text-align: center;
    white-space: nowrap;
    position: relative;
    height: 2em;
}

.sub_menu_inset {
    display: none;
    top: 0.5em;
    position: absolute;
    left: 0;
    width: 100%;
    background-color: #CCCCCC;
    word-spacing: 5em;
}

http://jsfiddle.net/u9v0mcvo/

Answer 1

Your menu's should be <ul> and the submenu should be <ul> inside the <li> s. The sub ul should then be positioned absolutely and display: none. the top level <li> s should have a :hover that changes the inner <ul> s to disbplay block.

Answer 2

You don't necessarily have to use <ul> and <li> elements. Although, you should avoid nesting <a> tags in <a> tags. I think this is what you might be trying to accomplish (hover over project):

http://jsfiddle.net/u9v0mcvo/1/

When making CSS-only drop downs, tooltips, or whatever, it helps to nest the initially hidden item in the element that is in charge of opening it.