I agree with a lot of what @anthony said but disagree on Wordpress being the best in scalability there @anthony. Not a founded conclusion and all opinion. That is, with, scaling meaning the ability of the application to support growth(by usage & functionality) through infrastructure & software.
When scaling, there's a whole lot more to consider than just the product.
Having used all three CMSs in different scenarios, some of the questions are:
1) what you want to use the CMS for (if mainly publishing - Wordpress, Joomla in that order. For more flexibility outside publishing - Drupal,Joomla in that order)
2) when you want to deliver (if requiring a quick prototype - Wordpress & Joomla would be better suited)
3) what your expertise/level of experience is (asker said html/css - Wordpress is best)
4) stability and support of the CMS(ALL are well-supported with good communities & 3rd party modules/extensions)
Without considering hosting environment & supporting tools (like memchached) in terms of developer-orientation(hence more power to scale), Drupal and Joomla far supersede Wordpress.
All three are market leaders in the CMS space but each has its favored audience/users.
- It is originally suited to publish-oriented sites (though can be extended).
- Wordpress is friendlier for the beginnner who wants a quick time to delivery over a good platform.
- Smoothest learning curve
- Very easy installation
- Joomla is reasonably beginner-friendly but also has a more flexible/powerful content structuring ability
- Moderate learning curve
- Easy installation
- More technically oriented than the other two. Not too difficult but one needs more understanding of product-specific features to achieve better ability to customise it
- Steepest learning curve amongst the two. The keyword of it all is "taxonomy". Understand that and you will harness its power
- No longer complicated setup a quick website
Where I would agree in part with anthony is investing in learning development. Learning PHP/MySQL would not be a wasted effort as you would be better able to customise.
For a beginner developer, knowing just HTML/CSS means alot of work & frustration getting it to do what you want.
I suggest you download ALL - Drupal, Joomla and Wordpress go to their online communities and post an INTELLIGENT question asking what would be best fitted for what you want to achieve. But do your research first on available 3rd party modules for the respective products. It is good netiquette to reflect an effort in most of these forums and no one wants to spoon feed.
Wordpress Forum - http://wordpress.org/support/
Drupal Forum - https://drupal.org/forum
Joomla Forum - http://forum.joomla.org/
You best friend should be Google: https://www.google.co.za/search?q=drupal+vs+joomla+vs+wordpress
From that you will see how there's no one answer.