title: HTML body is not at the top of the page even with margin set to 0
body: <p>This is a Ruby on Rails app and I can't get the body at the top of the page. Screenshot: <img src="https://i.stack.imgur.com/JPLLo.png" alt="Screenshot"></p>
  
  <p>I have no clue why this is happening as I've set all the properties correctly. <a href="https://github.com/WeeklyApps/blog" rel="noreferrer">Here is the source of the entire application.</a>  My view:</p>
  
  <pre><code>&lt;div id="header-wrap"&gt;
    &lt;div id="header"&gt;
      &lt;h1&gt;Blog&lt;/h1&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  
  &lt;div id="wrapper"&gt;
    &lt;div id="posts"&gt;
      &lt;% @posts.each do|post| %&gt;
      &lt;div id="post"&gt;
        &lt;h2&gt;&lt;%= post.title %&gt;&lt;/h2&gt;
        &lt;%= simple_format post.body %&gt;
        &lt;small&gt;
          &lt;%= link_to 'Edit', edit_post_path(post) %&gt; |
          &lt;%= link_to 'Destroy', post, method: :delete, data: { confirm: 'Are you sure?' } %&gt;
        &lt;/small&gt;
      &lt;/div&gt;
      &lt;% end %&gt;
    &lt;/div&gt;
  
    &lt;br&gt;
  
    &lt;%= link_to 'New Post', new_post_path %&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>My CSS (the commented out CSS is the hack I wrote to fix the issue by changing the positioning of the header-wrap and wrapper elements):</p>
  
  <pre><code>/*
   * This is a manifest file that'll be compiled into application.css, which will include all the files
   * listed below.
   *
   * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
   * or vendor/assets/stylesheets of plugins, if any, can be referenced here using a relative path.
   *
   * You're free to add application-wide styles to this file and they'll appear at the top of the
   * compiled file, but it's generally better to create a new file per style scope.
   *
   *= require_self
   *= require_tree .
   *= require twitter/bootstrap
   */
   html, body, {
      background-image:url('bg.png');
      background-color:#cccccc;
      padding: 0;
      margin: 0;
  }
  
  #header-wrap {
      background-color: #424242;
  /*  position: absolute;*/
      height: 100px;
      width: 100%;
    top: 0;
  }
  
  #header {
    margin: 0 auto;
      color: #FFFFFF;
      width: 588px;
  }
  
  #wrapper {
  /*  position: relative;
    top: 100px;*/
      padding: 0 6px;
      margin: 0 auto;
      width: 588px;
  }
  
  #posts {
  }
  
  #notice {
    color: green;
  }
  
  .field_with_errors {
    padding: 2px;
    background-color: red;
    display: table;
  }
  
  #error_explanation {
    width: 450px;
    border: 2px solid red;
    padding: 7px;
    padding-bottom: 0;
    margin-bottom: 20px;
    background-color: #f0f0f0;
    h2 {
      text-align: left;
      font-weight: bold;
      padding: 5px 5px 5px 15px;
      font-size: 12px;
      margin: -7px;
      margin-bottom: 0px;
      background-color: #c00;
      color: #fff;
    }
    ul li {
      font-size: 12px;
      list-style: square;
    }
  }
  </code></pre>