How to add Wrapper Div/container element around WordPress Widget Content

The register_sidebar function has 'before_widget' and 'after_widget' arguments that, by default, add <li> tags with a class of widget around each widget. You can change that in your theme to add an additional <div> around each widget if li.widget is not a good enough CSS Selector or if your theme removes it.

I don’t know what options are in the register_sidebar() function for your theme. You would have to change this code to fit your theme.

register_sidebar( array(
    'name'          => __( 'Sidebar name', 'theme_text_domain' ),
    'id'            => 'unique-sidebar-id',
    'description'   => __( 'Sidebar name description', 'theme_text_domain' ),
    'class'         => '',
    'before_widget' => '<li id="%1$s" class="widget %2$s"><div class="widget-content">',
    'after_widget'  => '</div></li>',
    'before_title'  => '<h2 class="widgettitle">',
    'after_title'   => '</h2>'
) );

---

Edit:

To isolate just the content, you could style everything in the widget and then style the title. For example, in the style sheet, do something like this:

.widget .widgettitle {
    /** Style the widget title. */
}

.widget {
    /** Style the whole widget. */
}

The .widget .wigettitle selector has greater specificity and will override the matching styles in .widget. The net effect is that only the widget content will be affected by the styles that are overridden.