Creating and editing a new theme.
To be able to create a theme, you first need administration privileges on the SMF install that you are using. Follow this route through your admin center:
Admininistration Center -> Theme and Layout Settings -> Install a New Theme
The Install a New Theme dialog contains 3 fields we have to look at. We can install a new theme from a file, from a directory on the server, or create a copy of the default theme. Since we're creating a new theme, we can ignore installing a theme from a file, or from a directory on the server, since these are mainly used for packed distributed themes.
We need the "Create a copy of Default named" field. Here, you can change the name to whatever you want, or you can leave it as it is. Click "Install!" and hit "OK" for any dialog boxes that may appear - your new theme should be up and running.
A copy of a default theme will not copy the whole theme - instead it just copies the following files:
If we wanted to change anything else, apart from the overall look of the forum header and footer or the stylesheet, we would have to add the corresponding file (or template) into our new theme's directory. Say you wanted to change something on the board index, or completely redesign it. You would need to copy BoardIndex.template.php from the default theme into your new theme's directory.
Themes "fall back" to the default version of a template if that template file cannot be found in the current theme's directory. This is why only 3 files are included in your new theme to begin with - if you're only dealing with, essentially, how the forum will look overall, the theme will pull the other template files and images from the default theme. This makes it a lot easier to upgrade your forum without having to rewrite the parts of your theme you didn't change anyway.
Editing Your New Theme
The new theme's name should now appear in the "Theme Settings" box, in the "Theme and Layout Settings" section of the admin panel. Click on it to get a list of theme-based options, where you can change the name of your theme, change basic aesthetic settings, edit options for all users and edit the main index template and style.css files.
Clicking on either "Modify the index template. (the main template)" or "Modify the style.css file. (colors, fonts, etc.)" will let you modify either index.template.php or style.css in your browser.
You can, if you prefer, edit these files in your html design/programming application on your computer. Just download your theme, edit as you wish, and upload it again. If you wish to change the look of more areas of your forum, you will need to download the files from your default theme, edit them, and upload them into your theme's directory