Chameleon bases on "styles_layout.css" from the standard theme and the one "user_styles.css"
The reason is one file is easier to handle by the Chameleon engine.
There are many ways to organize CSS files. Some big projects build even more modular CSS files sorted by function. If you are interested in a deeper discussion you may search in this forum for the topic.
Shortly mentioned - the separation into three files brings one big advantage when you update Moodle. The CSS files in the standard theme are always up to date. When you work with three files, you may keep the styles_layout.css from standard. With this file you are sure, that your theme will not break completely after a Moodle update. This technique has several times proven to be useful.
When you start working with Moodle theme design you may try to work with Chameleon, the interactive Moodle theme. To learn more you may search here in the forums or in Moodle Docs for Chameleon. Or click on the link in my profile
Chameleon and FireBug (a FireFox extension) are the tools of choice for my Moodle theme work.
The most up to date way to learn about and work with Moodle Themes is to use the interactive Chameleon theme together with Firefox and the FireBug extension.
How I use it:
1) Right click on the element and choose "inspect element" to see all attached CSS in FireBug.
2) Shift click on the element to get the Chameleon dialogue.
3) Click on exactly those tags which define the styling (FireBug shows them) in the Chameleon dialogue to select them.
4) Change/add the CSS with the Chameleon dialogue.
5) Save and immediately enjoy the Moodle pages with your newly set styling.
All documentation - how good it may be - can't be as actual as this method.
And FireBug shows the page structure and all attached CSS. You even can change the HTML and the CSS for short experiments on any page.
Have fun with your productive Moodle theme work.
The orangewhitepda was an early approach to offer support for small screen devices. It hardly ever has been used as I know.
The huge font sizes I have used to get better legibility when you set your device to render the table cells below each other. In the other themes the font size gets very small.
If you may creat a more actual and better solution you may consider giving it back to the Moodle community and we can see if we replace orangewhitepda.
Hello Uday,
this topic has been discussed several times. You may search for "section number" in the theme forum.
Hope this helps