5
Oh, wait, I see what you are saying. You aren't talking about theme layout, you are talking about adding additional content using one of the editors.
You do not need to use CSS, but, you would want to make sure nothing in the CSS for your theme is overriding your intended result.
One way to do this would be to put tags like this in your code:
<div class="custom">
a bunch of table stuff here
</div>
Then in the CSS for your theme you could add styles for your customer class.
If you prefer, you can add CSS at the tag level (but, it is sloppy). It is called and inline style... it defeats one of the advantages of CSS, so it's not recommended... but, OK.
You would add a style attribute, like this
<table style="position: relative; left: 10px; top: 10px;">
Either should work.