Index: src/wp-admin/load-styles.php
===================================================================
--- src/wp-admin/load-styles.php	(revision 36101)
+++ src/wp-admin/load-styles.php	(working copy)
@@ -3,50 +3,59 @@
 /**
  * Disable error reporting
  *
  * Set this to error_reporting( -1 ) for debugging
  */
 error_reporting(0);
 
 /** Set ABSPATH for execution */
 define( 'ABSPATH', dirname(dirname(__FILE__)) . '/' );
 define( 'WPINC', 'wp-includes' );
 
 require( ABSPATH . 'wp-admin/includes/noop.php' );
 require( ABSPATH . WPINC . '/script-loader.php' );
 require( ABSPATH . WPINC . '/version.php' );
 
-$load = preg_replace( '/[^a-z0-9,_-]+/i', '', $_GET['load'] );
+$load = $_GET['load'];
+if ( is_array( $load ) )
+	$load = implode( '', $load );
+
+$load = preg_replace( '/[^a-z0-9,_-]+/i', '', $load );
 $load = array_unique( explode( ',', $load ) );
 
 if ( empty($load) )
 	exit;
 
 $compress = ( isset($_GET['c']) && $_GET['c'] );
 $force_gzip = ( $compress && 'gzip' == $_GET['c'] );
 $rtl = ( isset($_GET['dir']) && 'rtl' == $_GET['dir'] );
 $expires_offset = 31536000; // 1 year
 $out = '';
 
 $wp_styles = new WP_Styles();
 wp_default_styles($wp_styles);
 
 foreach ( $load as $handle ) {
 	if ( !array_key_exists($handle, $wp_styles->registered) )
 		continue;
 
 	$style = $wp_styles->registered[$handle];
+
+	if ( ! $style->src ) {
+		continue;
+	}
+
 	$path = ABSPATH . $style->src;
 
 	if ( $rtl && ! empty( $style->extra['rtl'] ) ) {
 		// All default styles have fully independent RTL files.
 		$path = str_replace( '.min.css', '-rtl.min.css', $path );
 	}
 
 	$content = get_file( $path ) . "\n";
 
 	if ( strpos( $style->src, '/' . WPINC . '/css/' ) === 0 ) {
 		$content = str_replace( '../images/', '../' . WPINC . '/images/', $content );
 		$content = str_replace( '../js/tinymce/', '../' . WPINC . '/js/tinymce/', $content );
 		$content = str_replace( '../fonts/', '../' . WPINC . '/fonts/', $content );
 		$out .= $content;
 	} else {
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 36101)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -702,32 +702,48 @@ function wp_default_styles( &$styles ) {
 			$subsets .= ',greek,greek-ext';
 		} elseif ( 'vietnamese' == $subset ) {
 			$subsets .= ',vietnamese';
 		}
 
 		// Hotlink Open Sans, for now
 		$open_sans_font_url = "https://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,600italic,300,400,600&subset=$subsets";
 	}
 
 	// Register a stylesheet for the selected admin color scheme.
 	$styles->add( 'colors', true, array( 'wp-admin', 'buttons', 'open-sans', 'dashicons' ) );
 
 	$suffix = SCRIPT_DEBUG ? '' : '.min';
 
 	// Admin CSS
-	$styles->add( 'wp-admin',            "/wp-admin/css/wp-admin$suffix.css", array( 'open-sans', 'dashicons' ) );
-	$styles->add( 'login',               "/wp-admin/css/login$suffix.css", array( 'buttons', 'open-sans', 'dashicons' ) );
+	$styles->add( 'common',              "/wp-admin/css/common$suffix.css" );
+	$styles->add( 'forms',               "/wp-admin/css/forms$suffix.css" );
+	$styles->add( 'admin-menu',          "/wp-admin/css/admin-menu$suffix.css" );
+	$styles->add( 'dashboard',           "/wp-admin/css/dashboard$suffix.css" );
+	$styles->add( 'list-tables',         "/wp-admin/css/list-tables$suffix.css" );
+	$styles->add( 'edit',                "/wp-admin/css/edit$suffix.css" );
+	$styles->add( 'revisions',           "/wp-admin/css/revisions$suffix.css" );
+	$styles->add( 'media',               "/wp-admin/css/media$suffix.css" );
+	$styles->add( 'themes',              "/wp-admin/css/themes$suffix.css" );
+	$styles->add( 'about',               "/wp-admin/css/about$suffix.css" );
+	$styles->add( 'nav-menus',           "/wp-admin/css/nav-menus$suffix.css" );
+	$styles->add( 'widgets',             "/wp-admin/css/widgets$suffix.css" );
+	$styles->add( 'site-icon',           "/wp-admin/css/site-icon$suffix.css" );
+	$styles->add( 'l10n',                "/wp-admin/css/l10n$suffix.css" );
+
+	$styles->add( 'wp-admin', false, array( 'common', 'forms', 'admin-menu', 'dashboard', 'list-tables', 'edit', 'revisions', 'media', 'themes', 'about', 'nav-menus', 'widgets', 'site-icon', 'l10n', 'open-sans', 'dashicons' ) );
+
+	$styles->add( 'login',               "/wp-admin/css/login$suffix.css", array( 'buttons', 'forms', 'l10n', 'open-sans', 'dashicons' ) );
 	$styles->add( 'install',             "/wp-admin/css/install$suffix.css", array( 'buttons', 'open-sans' ) );
 	$styles->add( 'wp-color-picker',     "/wp-admin/css/color-picker$suffix.css" );
 	$styles->add( 'customize-controls',  "/wp-admin/css/customize-controls$suffix.css", array( 'wp-admin', 'colors', 'ie', 'imgareaselect' ) );
 	$styles->add( 'customize-widgets',   "/wp-admin/css/customize-widgets$suffix.css", array( 'wp-admin', 'colors' ) );
 	$styles->add( 'customize-nav-menus', "/wp-admin/css/customize-nav-menus$suffix.css", array( 'wp-admin', 'colors' ) );
 	$styles->add( 'press-this',          "/wp-admin/css/press-this$suffix.css", array( 'open-sans', 'buttons' ) );
 
 	$styles->add( 'ie', "/wp-admin/css/ie$suffix.css" );
 	$styles->add_data( 'ie', 'conditional', 'lte IE 7' );
 
 	// Common dependencies
 	$styles->add( 'buttons',   "/wp-includes/css/buttons$suffix.css" );
 	$styles->add( 'dashicons', "/wp-includes/css/dashicons$suffix.css" );
 	$styles->add( 'open-sans', $open_sans_font_url );
 
@@ -745,31 +761,33 @@ function wp_default_styles( &$styles ) {
 	$styles->add( 'imgareaselect',       '/wp-includes/js/imgareaselect/imgareaselect.css', array(), '0.9.8' );
 	$styles->add( 'wp-jquery-ui-dialog', "/wp-includes/css/jquery-ui-dialog$suffix.css", array( 'dashicons' ) );
 	$styles->add( 'mediaelement',        "/wp-includes/js/mediaelement/mediaelementplayer.min.css", array(), '2.18.1' );
 	$styles->add( 'wp-mediaelement',     "/wp-includes/js/mediaelement/wp-mediaelement.css", array( 'mediaelement' ) );
 	$styles->add( 'thickbox',            '/wp-includes/js/thickbox/thickbox.css', array( 'dashicons' ) );
 
 	// Deprecated CSS
 	$styles->add( 'media',      "/wp-admin/css/deprecated-media$suffix.css" );
 	$styles->add( 'farbtastic', '/wp-admin/css/farbtastic.css', array(), '1.3u1' );
 	$styles->add( 'jcrop',      "/wp-includes/js/jcrop/jquery.Jcrop.min.css", array(), '0.9.12' );
 	$styles->add( 'colors-fresh', false, array( 'wp-admin', 'buttons' ) ); // Old handle.
 
 	// RTL CSS
 	$rtl_styles = array(
 		// wp-admin
-		'wp-admin', 'install', 'wp-color-picker', 'customize-controls', 'customize-widgets', 'customize-nav-menus', 'ie', 'login', 'press-this',
+		'common', 'forms', 'admin-menu', 'dashboard', 'list-tables', 'edit', 'revisions', 'media', 'themes', 'about', 'nav-menus',
+		'widgets', 'site-icon', 'l10n', 'install', 'wp-color-picker', 'customize-controls', 'customize-widgets', 'customize-nav-menus',
+		'ie', 'login', 'press-this',
 		// wp-includes
 		'buttons', 'admin-bar', 'wp-auth-check', 'editor-buttons', 'media-views', 'wp-pointer',
 		'wp-jquery-ui-dialog',
 		// deprecated
 		'media', 'farbtastic',
 	);
 
 	foreach ( $rtl_styles as $rtl_style ) {
 		$styles->add_data( $rtl_style, 'rtl', 'replace' );
 		if ( $suffix ) {
 			$styles->add_data( $rtl_style, 'suffix', $suffix );
 		}
 	}
 }
 
@@ -1084,30 +1102,31 @@ function print_admin_styles() {
  *
  * @since 3.3.0
  *
  * @global WP_Styles $wp_styles
  * @global bool      $concatenate_scripts
  *
  * @return array|void
  */
 function print_late_styles() {
 	global $wp_styles, $concatenate_scripts;
 
 	if ( ! ( $wp_styles instanceof WP_Styles ) ) {
 		return;
 	}
 
+	script_concat_settings();
 	$wp_styles->do_concat = $concatenate_scripts;
 	$wp_styles->do_footer_items();
 
 	/**
 	 * Filter whether to print the styles queued too late for the HTML head.
 	 *
 	 * @since 3.3.0
 	 *
 	 * @param bool $print Whether to print the 'late' styles. Default true.
 	 */
 	if ( apply_filters( 'print_late_styles', true ) ) {
 		_print_styles();
 	}
 
 	$wp_styles->reset();
@@ -1118,64 +1137,68 @@ function print_late_styles() {
  * Print styles (internal use only)
  *
  * @ignore
  *
  * @global bool $compress_css
  */
 function _print_styles() {
 	global $compress_css;
 
 	$wp_styles = wp_styles();
 
 	$zip = $compress_css ? 1 : 0;
 	if ( $zip && defined('ENFORCE_GZIP') && ENFORCE_GZIP )
 		$zip = 'gzip';
 
-	if ( !empty($wp_styles->concat) ) {
+	if ( $concat = trim( $wp_styles->concat, ', ' ) ) {
 		$dir = $wp_styles->text_direction;
 		$ver = $wp_styles->default_version;
-		$href = $wp_styles->base_url . "/wp-admin/load-styles.php?c={$zip}&dir={$dir}&load=" . trim($wp_styles->concat, ', ') . '&ver=' . $ver;
+
+		$concat = str_split( $concat, 128 );
+		$concat = 'load%5B%5D=' . implode( '&load%5B%5D=', $concat );
+
+		$href = $wp_styles->base_url . "/wp-admin/load-styles.php?c={$zip}&dir={$dir}&" . $concat . '&ver=' . $ver;
 		echo "<link rel='stylesheet' href='" . esc_attr($href) . "' type='text/css' media='all' />\n";
 
 		if ( !empty($wp_styles->print_code) ) {
 			echo "<style type='text/css'>\n";
 			echo $wp_styles->print_code;
 			echo "\n</style>\n";
 		}
 	}
 
 	if ( !empty($wp_styles->print_html) )
 		echo $wp_styles->print_html;
 }
 
 /**
  * Determine the concatenation and compression settings for scripts and styles.
  *
  * @since 2.8.0
  *
  * @global bool $concatenate_scripts
  * @global bool $compress_scripts
  * @global bool $compress_css
  */
 function script_concat_settings() {
 	global $concatenate_scripts, $compress_scripts, $compress_css;
 
 	$compressed_output = ( ini_get('zlib.output_compression') || 'ob_gzhandler' == ini_get('output_handler') );
 
 	if ( ! isset($concatenate_scripts) ) {
 		$concatenate_scripts = defined('CONCATENATE_SCRIPTS') ? CONCATENATE_SCRIPTS : true;
-		if ( ! is_admin() || ( defined('SCRIPT_DEBUG') && SCRIPT_DEBUG ) )
+		if ( ( ! is_admin() && ! did_action( 'login_init' ) ) || ( defined('SCRIPT_DEBUG') && SCRIPT_DEBUG ) )
 			$concatenate_scripts = false;
 	}
 
 	if ( ! isset($compress_scripts) ) {
 		$compress_scripts = defined('COMPRESS_SCRIPTS') ? COMPRESS_SCRIPTS : true;
 		if ( $compress_scripts && ( ! get_site_option('can_compress_scripts') || $compressed_output ) )
 			$compress_scripts = false;
 	}
 
 	if ( ! isset($compress_css) ) {
 		$compress_css = defined('COMPRESS_CSS') ? COMPRESS_CSS : true;
 		if ( $compress_css && ( ! get_site_option('can_compress_scripts') || $compressed_output ) )
 			$compress_css = false;
 	}
 }
Index: Gruntfile.js
===================================================================
--- Gruntfile.js	(revision 36101)
+++ Gruntfile.js	(working copy)
@@ -81,39 +81,56 @@ module.exports = function(grunt) {
 							'!wp-includes/js/backbone.js',
 							'!wp-includes/js/underscore.js',
 							'!wp-includes/js/jquery/jquery.masonry.js',
 							'!wp-includes/js/jquery/ui/*.js',
 							'!wp-includes/js/tinymce/tinymce.js',
 							'!wp-includes/version.php' // Exclude version.php
 						],
 						dest: BUILD_DIR
 					},
 					{
 						src: 'wp-config-sample.php',
 						dest: BUILD_DIR
 					}
 				]
 			},
-			'wp-admin-rtl': {
+			'wp-admin-css-compat-rtl': {
 				options: {
 					processContent: function( src ) {
 						return src.replace( /\.css/g, '-rtl.css' );
 					}
 				},
 				src: SOURCE_DIR + 'wp-admin/css/wp-admin.css',
 				dest: BUILD_DIR + 'wp-admin/css/wp-admin-rtl.css'
 			},
+			'wp-admin-css-compat-min': {
+				options: {
+					processContent: function( src ) {
+						return src.replace( /\.css/g, '.min.css' );
+					}
+				},
+				files: [
+					{
+						src: SOURCE_DIR + 'wp-admin/css/wp-admin.css',
+						dest: BUILD_DIR + 'wp-admin/css/wp-admin.min.css'
+					},
+					{
+						src:  BUILD_DIR + 'wp-admin/css/wp-admin-rtl.css',
+						dest: BUILD_DIR + 'wp-admin/css/wp-admin-rtl.min.css'
+					}
+				]
+			},
 			version: {
 				options: {
 					processContent: function( src ) {
 						return src.replace( /^\$wp_version = '(.+?)';/m, function( str, version ) {
 							version = version.replace( /-src$/, '' );
 
 							// If the version includes an SVN commit (-12345), it's not a released alpha/beta. Append a date.
 							version = version.replace( /-[\d]{5}$/, '-' + grunt.template.today( 'yyyymmdd' ) );
 
 							/* jshint quotmark: true */
 							return "$wp_version = '" + version + "';";
 						});
 					}
 				},
 				src: SOURCE_DIR + 'wp-includes/version.php',
@@ -142,50 +159,51 @@ module.exports = function(grunt) {
 		browserify: mediaConfig,
 		sass: {
 			colors: {
 				expand: true,
 				cwd: SOURCE_DIR,
 				dest: BUILD_DIR,
 				ext: '.css',
 				src: ['wp-admin/css/colors/*/colors.scss'],
 				options: {
 					outputStyle: 'expanded'
 				}
 			}
 		},
 		cssmin: {
 			options: {
-				'wp-admin': ['wp-admin', 'color-picker', 'customize-controls', 'customize-widgets', 'customize-nav-menus', 'ie', 'install', 'login', 'press-this', 'deprecated-*'],
 				compatibility: 'ie7'
 			},
 			core: {
 				expand: true,
 				cwd: SOURCE_DIR,
 				dest: BUILD_DIR,
 				ext: '.min.css',
 				src: [
-					'wp-admin/css/{<%= cssmin.options["wp-admin"] %>}.css',
+					'wp-admin/css/*.css',
+					'!wp-admin/css/wp-admin*.css',
 					'wp-includes/css/*.css'
 				]
 			},
 			rtl: {
 				expand: true,
 				cwd: BUILD_DIR,
 				dest: BUILD_DIR,
 				ext: '.min.css',
 				src: [
-					'wp-admin/css/{<%= cssmin.options["wp-admin"] %>}-rtl.css',
+					'wp-admin/css/*-rtl.css',
+					'!wp-admin/css/wp-admin*.css',
 					'wp-includes/css/*-rtl.css'
 				]
 			},
 			colors: {
 				expand: true,
 				cwd: BUILD_DIR,
 				dest: BUILD_DIR,
 				ext: '.min.css',
 				src: [
 					'wp-admin/css/colors/*/*.css'
 				]
 			}
 		},
 		rtlcss: {
 			options: {
@@ -635,31 +653,32 @@ module.exports = function(grunt) {
 
 		grunt.task.run( '_' + this.nameArgs );
 	} );
 
 	grunt.registerTask( 'precommit', 'Runs front-end dev/test tasks in preparation for a commit.', [
 		'postcss:core',
 		'imagemin:core',
 		'browserify',
 		'jshint:corejs',
 		'uglify:bookmarklet',
 		'qunit:compiled'
 	] );
 
 	grunt.registerTask( 'copy:all', [
 		'copy:files',
-		'copy:wp-admin-rtl',
+		'copy:wp-admin-css-compat-rtl',
+		'copy:wp-admin-css-compat-min',
 		'copy:version'
 	] );
 
 	grunt.registerTask( 'build', [
 		'clean:all',
 		'copy:all',
 		'cssmin:core',
 		'colors',
 		'rtl',
 		'cssmin:rtl',
 		'cssmin:colors',
 		'uglify:core',
 		'uglify:embed',
 		'uglify:jqueryui',
 		'concat:tinymce',
Index: src/wp-admin/css/login.css
===================================================================
--- src/wp-admin/css/login.css	(revision 36101)
+++ src/wp-admin/css/login.css	(working copy)
@@ -1,18 +1,15 @@
-@import url(forms.css);
-@import url(l10n.css);
-
 html,
 body {
 	height: 100%;
 	margin: 0;
 	padding: 0;
 }
 
 html {
 	background: #f1f1f1;
 }
 
 body {
 	background: #f1f1f1;
 	min-width: 0;
 	color: #444;
Index: src/wp-login.php
===================================================================
--- src/wp-login.php	(revision 36101)
+++ src/wp-login.php	(working copy)
@@ -56,49 +56,50 @@ function login_header( $title = 'Log In'
 	if ( $shake_error_codes && $wp_error->get_error_code() && in_array( $wp_error->get_error_code(), $shake_error_codes ) )
 		add_action( 'login_head', 'wp_shake_js', 12 );
 
 	?><!DOCTYPE html>
 	<!--[if IE 8]>
 		<html xmlns="http://www.w3.org/1999/xhtml" class="ie8" <?php language_attributes(); ?>>
 	<![endif]-->
 	<!--[if !(IE 8) ]><!-->
 		<html xmlns="http://www.w3.org/1999/xhtml" <?php language_attributes(); ?>>
 	<!--<![endif]-->
 	<head>
 	<meta http-equiv="Content-Type" content="<?php bloginfo('html_type'); ?>; charset=<?php bloginfo('charset'); ?>" />
 	<title><?php bloginfo('name'); ?> &rsaquo; <?php echo $title; ?></title>
 	<?php
 
-	wp_admin_css( 'login', true );
+	wp_enqueue_style( 'login' );
 
 	/*
 	 * Remove all stored post data on logging out.
 	 * This could be added by add_action('login_head'...) like wp_shake_js(),
 	 * but maybe better if it's not removable by plugins
 	 */
 	if ( 'loggedout' == $wp_error->get_error_code() ) {
 		?>
 		<script>if("sessionStorage" in window){try{for(var key in sessionStorage){if(key.indexOf("wp-autosave-")!=-1){sessionStorage.removeItem(key)}}}catch(e){}};</script>
 		<?php
 	}
 
 	/**
 	 * Enqueue scripts and styles for the login page.
 	 *
 	 * @since 3.1.0
 	 */
 	do_action( 'login_enqueue_scripts' );
+
 	/**
 	 * Fires in the login page header after scripts are enqueued.
 	 *
 	 * @since 2.1.0
 	 */
 	do_action( 'login_head' );
 
 	if ( is_multisite() ) {
 		$login_header_url   = network_home_url();
 		$login_header_title = get_current_site()->site_name;
 	} else {
 		$login_header_url   = __( 'https://wordpress.org/' );
 		$login_header_title = __( 'Powered by WordPress' );
 	}