CSS div is not visible

Question

With this css

.addProblemClass{
    width:300px;
    height:300px;
    border:solid 1px #000000;
    background-color:#FFFFFF;
    opacity:0.9;/*For chrome and mozilla*/
    filter:alpha(opacity=90);/*For IE*/
}

.boxHeader{
    border: solid 1px #000000;
    height: 15%;
}

.addProblemHeaderTextDiv{
    border:solid 1px #FF0000;
    margin:-1px;
    width: 80%;
    height: 100%;
    float: left;
}

.addProblemHeaderImageDiv{
    border:solid 1px #00FF00;
    margin:-1px;
    float: left;
    width: 20%;
    height: 100%;
}

boxBody{
    border:solid 1px #0000FF;
    margin: -1px 0px;
    height: 85%;
    width: 100%;
}

and this html

<div class="addProblemClass">
            <div class="boxHeader">
                <div class="addProblemHeaderImageDiv"></div>//DIV A
                <div class="addProblemHeaderTextDiv"></div>//DIV B
            </div>
            <div class="boxBody"></div>//DIV C
        </div>

DIV C is not visible. Any ideas for the reason why this is hapenning? Thank you

Answer 1

because DivC has % width and height, but as it contains nothing the percentage is a percentage of 0 which will always be 0

edit: make it a fixed width like px or em and it will show, or add some content into it.

Answer 2

Add a . before boxBody in css ..

.boxBody{
}