Don't know about joomla, but w/wp you can create custom pages/templates so you should be able to apply their design.
Easiest way would be to use a child theme.
In the same folder where you have the parent theme. Normally wp-content>themes. You'll find the standard themes in their respective folders.
The newest is "twentyfourteen" or you can choose another parent theme.
Add a new folder there.
Call it whatever you want to for example "myClientsTheme" in that folder you can add the php files you want to override, And your own css. In that new css file, to declare it a child theme you want at the top
<font color='"#B22222"'>Theme Name: myClientsTheme</font>
<font color='"#A52A2A"'>Template: twentyfourteen</font>
or you can c&p the entire style sheet and have full control of it.
The you can create you own custom tempate.
for example copy the index.php from 2014 to your new folder or any file you will be overriding. of course you rename it whatever you want to. for example. page1.php or home.php
and at the top of that file add
<font color='"#B22222"'>//Template Name: whatever you want to name it</font>
and change the code however you wish it.
in the wp admin you create a page. Select the new template & publish it.
There are more details, that was very very basic. But if you want to try that'll get you started i think.