Css on posts not working

i am developing a template and i am having some problems i am a newbie when comes to coding here is what is going on:

i have created a css files called style.css and added the following:
what i want to do is a css to control every post in my page and assign different colors to each divs but the color divs are not showing up.

The CSS code:

.PostBackground1 {
	 background-color: #FF8000;
}
.PostBackground2 {
	 background-color: #F9DBFB;
}

the index.php code:

and then in my code i add all this to show the post in a loop:

<?php if (have_posts()) : ?>
<?php $count = 0; ?>
<?php while (have_posts()) : the_post(); ?>
<?php $count++; ?>
<?php if ($count == 1) : ?>

 <!-- the problem below is that i use the div class and it did not change the post background -->

<div class="PostBackground1">
<h1><?php the_title(); ?></h1>
<?php the_content(); ?>
</div>

<!-- end of first post loop going to second loop -->

<?php elseif ($count == 2) : ?>     

<div class="PostBackground2">
<h1><?php the_title(); ?></h1>
<?php the_content(); ?>
</div>

any advices? im having a headacke =)