Edit in JSFiddle

<div id="container">

<div id="dashboard">
    <ul class="menu">
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_bet01.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_bet03.png"></a></li>
    </ul>
    <ul class="menu">
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_table01.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_table02.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_table03.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_table04.png"></a></li>
    </ul>
    <ul class="menu">
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_chair01.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_chair02.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_chair03.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_chair04.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_chair05.png"></a></li>
        <li><a class="icon" href="#"><img src="http://iideacraft.com/blog-img/icon_chair06.png"></a></li>
    </ul>
</div>

</div>

body {
    background: #37495e;
}

#container {
    width: 80%;
    margin: 50px auto;
}

#dashboard {
    padding: 20px;
}


.menu {
	display: table;
	width: 100%;
}

.menu li {
	display: table-cell;
    vertical-align: top;
}

.menu li {
	border-top: 2px solid #2c3c50;
	border-right: 2px solid #2c3c50;
}

.icon {
    display: block;
    padding: 20px;
    text-align: center;
    border-top: 2px solid #415266;
    border-right: 2px solid #415266;
}


.icon img {
    width: 100%;
    vertical-align: bottom;
}

.icon img:hover {
    opacity: .5;
}

.menu:first-child li,
.menu:first-child .icon {
    border-top-color: transparent;
}

.menu li:last-child,
.menu li:last-child .icon {
    border-right-color: transparent;
}