Hi Vladimir!

Generally, it’s best to post to the forum for the plugin you’re working on whenever possible. For WP-Polls, that would be here:

https://wordpress.org/support/plugin/wp-polls

I did take a peek at your site. Rather than trying to change the templates, I’d recommend using a bit of CSS to change the background color of the entire widget.

Using my browser inspector, I can see the widget on your site has an ID of #polls-widget-2

So you should be able to use the following CSS:

#polls-widget-2 {
    background: #f44336;
    padding: 48px 10px 24px;
}

The background color changes the color as you requested. The padding keeps the same top and bottom padding the widget always had, but also adds a little bit to the sides so the text doesn’t run right up against the edge of the red block 🙂

A good way to add CSS on your site is to use the Additional CSS panel in the Customizer (assuming you’re running at least WordPress 4.7) or with something like the Jetpack Plugin using the Custom CSS Module.

Let me know how that looks!