if your theme uses body_class() then you could add a section to style.css of your theme, with styles all beginning with .page-id-4 to target page specific styles;
if not, and you want to load the specific styles after the general style.css, you could create a style-4.css (the name does not really matter, but has to be referenced in the conditional code) and add a conditional section to header.php, after the linking of the other stylesheet;
example:
<?php if( is_page(4) ) { ?>
<link rel="stylesheet" href="<?php echo get_stylesheet_directory_uri(); ?>/style-4.css" type="text/css" media="screen" />
<?php } ?>
if the style-4.css is saved in the /css sub-folder in your theme, then the link should be:
<link rel="stylesheet" href="<?php echo get_stylesheet_directory_uri(); ?>/css/style-4.css" type="text/css" media="screen" />
if you want/need to load the specifi stylesheet instead of style.css, then change the existing stylesheet link ( usually some line like: <link rel="stylesheet" href="<?php bloginfo('stylesheet_url'); ?>" type="text/css" media="screen" /> or similar in header.php of your theme) into some code like this:
<?php if( is_page(4) ) { ?>
<link rel="stylesheet" href="<?php echo get_stylesheet_directory_uri(); ?>/style-4.css" type="text/css" media="screen" />
<?php } else { ?>
<link rel="stylesheet" href="<?php bloginfo('stylesheet_url'); ?>" type="text/css" media="screen" />
<?php } ?>