CSS not being read

Hi. I’m trying to adjust the height of my logo in the header through CSS, but it doesn’t work – whatever I do, no changes are being made. If I make some very drastic changes, like completely delete the code, then I see the effect, but not otherwise. What could it be?

Here’s an excerpt from header.php:

<div class="logo-wrap">
						<?php if ($mts_options['mts_logo'] != '') { ?>
							<?php if( is_front_page() || is_home() || is_404() ) { ?>
									<h1 id="logo" class="image-logo">
										<a href="<?php echo home_url(); ?>"><img src="<?php echo $mts_options['mts_logo']; ?>" alt="<?php bloginfo( 'name' ); ?>"></a>
									</h1><!-- END #logo -->

This is CSS:

#logo a:hover { color: #222 }
.image-logo { margin-top: 10px }
#logo img { float: left }
.logo-wrap {
    padding: 15px 0;
    overflow: hidden;
    float: left;
    margin: 15px 0 0;
}

To adjust the height of the header, I can use margins, right? But no matter what I put in there, it doesn’t affect anything. I can affect some other parts of the website through this same CSS code though.

What could be the reason?