I have this scenario:

```
<div id="parent">
   <div id="a"></div>
   <li class="b"></li>
</div>

```

In my case, I want to add margin-top: 5px; to class b only if it is after id a. Note that these are not children, but within the same element. 

I would like an approach using pure CSS or CSS3 and without the need to use LESS or SASS. I know that this might be possible using JavaScript or jQuery as well, was just wondering if it can be done in CSS and how.