The newer versions of SimpleMenu allows for an easy way of adding custom themes.
There are two main ways to add new SimpleMenu themes:
1. In the simplemenu themes folder;
2. In your theme folder.
If you look under the simplemenu folder, you will see a sub-folder named themes. You can place your own specialized themes in that folder to make them available system-wide (i.e. if you are using many themes or use one Drupal installation for many websites.) In other words, this folder is viewed as a global theme folder.
The themes folder expect a sub-folder with the name of the theme and at least one CSS file with the same name and the .css extension:
simplemenu/themes/<my_theme>/<my_theme>.css
The folder may include other files such as images of arrows replacing the default simplemenu system icons.
In order for your theme to be used, go to the main SimpleMenu settings screen and choose your theme as the SimpleMenu theme. If you already had the window open when installation the theme sub-folder, it will not appear in the list. Reload the page and you will now see it.
Make sure to save your changes.
Now SimpleMenu uses your CSS file.
You have two ways to make the CSS of a specific theme work with SimpleMenu.
This method is what is used in most cases. You can overwrite all the CSS entries from the default SimpleMenu themes in your theme style.css files. This way you make sure that your look will work in all situation.
This method is quite useful as it requires no changes to the SimpleMenu settings and thus the default SimpleMenu theme will automatically kick in as required (i.e. Administration theme, etc.)
This method allows you to completely avoid the SimpleMenu CSS file. This is a selection available in the SimpleMenu settings screen.
The difference between the Custom Theme and the Overwriting method is that the custom theme does not require you to overwrite every single CSS entry. Therefore, it simplifies the handling of the CSS greatly.
It is otherwise very similar to Overwriting.
Note that in this case switching between themes may cause a problem since only themes that now have SimpleMenu CSS data will work properly. Other themes will show the menu unthemed.
New themes are very welcome. Please, attach them to the SimpleMenu issue queue.
If you create a special theming for your own theme, simply check those changes to your theme CVS repository. You may want to let people know that they need to use Custom Theme if you do not overwrite all the CSS from the default simplemenu stylesheets.