Styled divs not appearing

Why is the following CSS code not working with these divs? They don't seem to appear at all when I open the site although everything else on the external CSS file on my HTML file is working in divs...

Any help would be greatly appreciated, Thank you!

CSS:

.leftAd
{

width: 200px;
height: 300px;   
padding: 5px;
border: 3px solid black;
text-align: center;
margin-left: 4%;
margin-right: 15%;
border-radius: 10px; 
background-color: white;

}

.rightAd
{

width: 200px;
height: 300px;   
padding: 5px;
border: 3px solid black;
text-align: center;
margin-right: 4%;
border-radius: 10px; 
background-color: white;

}

.rightAlign
{

float: right;

}

CSS Continued:

.leftAlign
{

float: left;

}

.text
{

font-family: text;
font-size: 25px;
color: white; 

}

HTML

<div class="leftAd leftAlign text"></div> 

<iframe width="420" height="315" src="https://www.youtube.com/embed/C0DPdy98e4c" frameborder="0" allowfullscreen></iframe>

<div class="rightAd rightAlign text"></div>