I have an HTML document that I want to display a simple list horizontally. There is a plethora of examples on how to do this, but my list will not display horizontally:

HTML:

```
<div id="main_menu">
   <ul>
      <li><a href="#1">Link 1</a></li>
      <li><a href="#2">Link 2</a></li>
      <li><a href="#3">Link 3</a></li>
   </ul>
</div>

```

CSS:

```
#main_menu ul{  
    margin: 0;
    padding: 0;
    list-style-type: none;

}

```

What am I not understanding - why is it not displaying horizontally?

I am testing in Chrome.