Just some basic pointers.
There are two main ingredients for mod-suffixes.

The html that is used in the modChrome. Think of it what directly surrounds the module you publish. You can check the modules.php in the html folder of your template for that.

this is the "standard"-modChrome:

function modChrome_standard($module, &$params, &$attribs)
{
if (!empty ($module->content)) : ?>
<?php if ($params->get('moduleclass_sfx')!='') : ?>
<div class="<?php echo $params->get('moduleclass_sfx'); ?>">
<?php endif; ?>
<div class="rt-block">
<?php if ($module->showtitle != 0) : ?>
<div class="module-title">
<h2 class="title"><?php echo $module->title; ?></h2>
</div>
<?php endif; ?>
<?php echo $module->content; ?>
</div>
<?php if ($params->get('moduleclass_sfx')!='') : ?>
</div>
<?php endif; ?>
<?php endif;
}

The modChrome is set via this piece of code in index.php
<?php echo $gantry->displayModules('top','standard','standard'); ?>
The 2nd "standard" is the one that sets the chrome.

Now you can see that the chrome is much simpler as it is in the club-releases.
In the club releases we also have divs like <div class="module-surround">
that can be used for styling.

In the modChrome

<div class="<?php echo $params->get('moduleclass_sfx'); ?>">

is pulling the mod-suffix.

So checking the code you see there is .rt-block in that code-block.
We can use that now. (if you really want to get into I would add an element just for the mod-suffix.)

Just to give an example:
Here is the code for three mod-suffixes.
One that adds rounded corners and two add background colors ...

div.suffix-1 div.rt-block {
background-color: maroon;
color: white;
}

div.rounded div.rt-block {
-webkit-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px
}

div.suffix-2 div.rt-block {
background-color: red;
color: white;
}

they can be used as a mod-suffix in a combination like this:
"suffix-2 rounded"

I hope this helps. Of course it's just the beginning. Check out the latest templates to see what other cool things you can do. The suffix can also be used as a toggle to inject html-elemnts to the module chrome for icons, badges etc ...

GoG wrote:

because there is no
<div id="rt-content-top-a">...</div> in the code.
If it doesn't exist you can't style it.

When you create mod-suffixes you have to look into the generated html-structure wich gives you the hooks to style ...

GoG wrote:
Can you give me a link where I can check this?