title: Centering with margin:auto does not work
body: <p>I want to position my paragraph (title) into the middle of the div, but margin:auto; does absoulutely nothing. </p>
  
  <pre><code>#header {
    background-color: lime;
    height: 100px;
    width: 90%;
    margin: 0px auto;
    border: 1px solid grey;
  #title {
    margin-top: 10px;
    margin-left: auto;
    margin-right: auto;
    text-align: center;
    height: 50px;
    border: 1px solid grey;
    width: 300px;
    display: inline-block; 
    text-transform: uppercase;
    font-size: 30px; 
    color: blue;
  </code></pre>
  
  <p>As you can see, both width and heights are defined, the paragraph does behave as a block element, so I really don't understand why is it still not centered in the middle of the div... Btw, the margin:auto did work for the divider, just not for the paragraph inside the divider. </p>