how to style wp admin

wp-admin-plugin

You make a plugin, then add a wp-admin.css to the folder.  Here's some sample code for both the php and the css.
reference: http://codex.wordpress.org/Creating_Admin_Themes

blah-blah-admin-theme.php:
<?php

/*
Plugin Name: Client-Name Admin Theme
Plugin URI: http://techliminal.com
Description: Client-name Admin Theme, styling for the administration screens for Properties
Author: Tech Liminal
Version: 1.0
Author URI: http://techliminal.com
*/

function clientname_admin_theme_style() {
    wp_enqueue_style('clientname-admin-theme', plugins_url('wp-admin.css', __FILE__));

}
add_action('admin_enqueue_scripts', 'clientname_admin_theme_style');
add_action('login_enqueue_scripts', 'clientname_admin_theme_style');

?>

wp-admin.css:

#postbox-container-2 h2 {
  border: 1px solid rgb(213, 213, 213);
  font-weight: bold;
  padding: 4px;
}
#postbox-container-2 h3 {
  font-size:20px;
}

#postbox-container-2 {
  font-size: 12px;
}
#postbox-container-2 label {
  clear: left;
  float: left;
  font-size: 15px;
  font-weight: bold;
  margin: 7px 0 0;
  width: 100px;
}

#postbox-container-2 textarea {
  font-size:14px;
  width:500px;
  margin: -9px 0 0 0;
}

#postbox-container-2 p.col-3 span {
  margin: 0 0 0 157px;
}

#postbox-container-2 select {
padding: 2px;
height: 2em;
margin: 8px 20px 18px -14px
}

.admin-chk {
  font-size: 14px;
  padding: 0 2px 0 10px;
}

.admin-select label{
  
}

.admin-select p {
  float:left;
}