Editing search box

Hello,
How do I make the search box smaller? (Width-wise)
This is the code I’m using for the search box

<?php 	/* Widgetized sidebar, if you have the plugin installed. */
					if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar() ) : ?><ul>
			<li>
				<?php get_search_form(); ?> <?php endif; ?>
			</li></ul>

Is there any way I could edit it through CSS? If so, how do I edit the php code?

Thanks in advance.