hello world drupal module exercise

hello_world.css

body.node-type-article .field-name-body p:first-child:before {
  content: "Content starts here! ";
  font-style: italic;
  display: block;
}

body.node-type-article #content:after {
  content: "Hello World!";
  font-weight: bold;
  font-size: 150%;
  position: fixed;
  top: 50%;
  right: 10px;
  -webkit-transform: rotate(90deg);
  writing-mode: tb-rl;
}

hello_world.info

name = hello world
description = prints "hello world" and "content starts here" on article pages (mc module challenge)
core = 7.x
package = Module Challenge
stylesheets[all][] = hello_world.css

hello_world.module

<?php

/** 
 * Nothing to see here, this  is a css-only module
 */