The screenshot shows the name of the skin is 'WowMusic' which looks like its based off of Flashback by the rest of the screen.
make sure your CSS files are registered in your include.php file for your skin and that they are in the /css directory.
function jrFlashback_skin_init(){
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'html.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'grid.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'site.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'page.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'banner.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'header.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'footer.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'form_element.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'form_input.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'form_select.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'form_layout.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'form_button.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'form_notice.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'forum.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'list.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'menu.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'table.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'tabs.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'image.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'gallery.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'profile.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'skin.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'slider.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'text.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'bundle.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'base.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'action.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'doc.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'poll.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'slidebar.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'admin_menu.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'admin_log.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'admin_modal.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'tablet.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'mobile.css');
jrCore_register_module_feature('jrCore', 'css', 'jrFlashback', 'playlist.css');
jrCore_register_module_feature('jrCore', 'javascript', 'jrFlashback', 'responsiveslides.min.js');
jrCore_register_module_feature('jrCore', 'javascript', 'jrFlashback', 'jrFlashback.js');
jrCore_register_module_feature('jrCore', 'javascript', 'jrFlashback', APP_DIR . '/skins/jrFlashback/contrib/slidebars/slidebars.min.js');
jrCore_register_module_feature('jrCore', 'icon_color', 'jrFlashback', 'white');
jrCore_register_module_feature('jrCore', 'icon_size', 'jrFlashback', 16);
jrCore_register_module_feature('jrCore', 'module_icons', 'jrFlashback', 'show', false);
jrCore_register_module_feature('jrCore', 'media_player_skin', 'jrFlashback', 'jrAudio', 'jrAudio_player_dark');
jrCore_register_module_feature('jrCore', 'media_player_skin', 'jrFlashback', 'jrVideo', 'jrVideo_player_dark');
jrCore_register_module_feature('jrCore', 'media_player_skin', 'jrFlashback', 'jrPlaylist', 'jrPlaylist_player_dark');
return true;
}
There are some javascript files too. those will all be packaged up into a single file to increase page load time.
Take a look inside some of those files too to see the convention for getting a CSS property into the STYLE tab.
That commented stuff at the top of the CSS is what will show in the STYLE tab (screenshot). The properties with /* @ignore */ will not show up.