Hi @walkysss,
1. First, you can open file templatesja_magz_iicontenttypeformsarticle_edit.xml then look for this code and add more option there :
<field name="ctm_article_style" type="list"
default="default"
label="TPL_MOD_ARTICLES_CATEGORY_COLOUMN"
description="TPL_MOD_ARTICLES_CATEGORY_COLOUMN_DESC">
<option value="default">Default</option>
<option value="dark">Dark</option>
<option value="image">Image Background</option>
</field>
2. Next, open file templatesja_magz_iicsscustom.css (if you don’t have this file, just create a new one) and add custom CSS rule for you new style.