I have two inner divs which are nested inside a wrapper div. I want the two inner div's to get arranged one below the other. But as of now they are getting arranged on the same line. 

```css
#wrapper{
        margin-left:auto;
        margin-right:auto;
        height:auto; 
        width:auto;
    }
    #inner1{
        float:left; 
    }
    #inner2{
        float:left; 
    } 

```

```html
  <div id="wrapper">
        <div id="inner1">This is inner div 1</div>
        <div id="inner2">This is inner div 2</div>
    </div>
```