How to change size of rss feed icon on the SEO Basics theme?

I’d like to change the size of the rss feed icon in the sidebar on the SEO Basics theme on my site. I think I need to indicate the size in the CSS, but don’t know how. Can anyone provide guidance/instructions?
Thank you.

Here’s the CSS that mentions “rss”:
#header-rss {
float: right;
margin-right: 10px;
}

.entry-title {
margin: 0;
padding: 0;
}

.entry-title a {
color: #F58E0E
}

.sidebar, .sidebar a, .entry-date, .entry-meta, .entry-meta a {
color: #666;
}

#rss_icon {
padding: 1em;
}

#rss_icon span {
font-size: 1.5em;
font-weight: bold;
line-height: 62px;
}

#rss_icon img {
float: right;
}

Here’s the code from the sidebar.php:
<li id=”rss_icon”><div>
‘ title='<?php _e(‘Subscribe to feed’, ‘sds’) ?>’>
<img src='<?php bloginfo(‘template_directory’) ?>/images/rssfeedicon.jpg’ alt='<?php _e(‘Subscribe to feed’, ‘sds’) ?>’ />

<span><?php _e(‘Subscribe to feed’, ‘sds’) ?></span>
</div><div class=’clear’></div>