Where can i find styles in joomla?

Question

Joomla

Hello! Tell me pliz, already searched. I didn’t work with Joomla, but I need to adapt the site on it for a mobile phone. There is a button called like this:

<jdoc:include type="modules" name="calc" style="xhtml" />

The output is the following:

<div class="moduletable">
      
<div class="custom">
<nobr>
<a href="/rasschitat-stoimost" title="Рассчитать стоимость" class="online_podbor">Онлайн-подбор</a>
</nobr>...

Where can I find styles for the online_podbor class, I don’t understand, and how is this button formed in general? It would be logical if there would be some kind of calc module or component, but it is not.
Also, please tell me where static pages can be, I won’t find them either!