I might have been staring at the computer screen too long today and looked over something small but why can I not target these individual cells? (a1, a2, a3, etc...)
<div class="row-a">
    <div class="a">
        <div class="1"></div>
            sdf
    </div>
    <div class="a">
        <div class="2"></div>
    </div>
    <div class="a">
        <div class="3"></div>
    </div>
    <div class="a">
        <div class="4"></div>
    </div>
    <div class="a">
        <div class="5"></div>
    </div>
    <div class="a">
        <div class="6"></div>
    </div>
    <div class="a">
        <div class="7"></div>
    </div>
    <div class="a">
        <div class="8"></div>
    </div>
    <div class="a">
        <div class="9"></div>
    </div>
    <div class="a">
        <div class="10"></div>
    </div>
</div>
CSS:
div.row-a div.a div.1 {
    border: 1px solid green;
    margin-left: 5px;
    margin-top: 5px;
    background-color:red;
    height: 50px;
    width: 50px;
}
jsFiddle: http://jsfiddle.net/tuHLE/
 
     
     
    