Astrid theme background widget colot

I am trying to change the background color of my widget on the sidebar of my website. When I use the code below nothing happens to the widget.

.custom_html-4 {
background-color: red;
}

link to my site http://pffrj.hosts.cx/

Any help would be appreciated.

Hi,

You should use this code instead:

#secondary.widget-area .widget {
    background-color: red;
}

Regards,