[Theme Horse Support Team]

Hi
Hope this may help you
just add this in your child theme style.css
For example:-

/*
Theme Name: interface Child Theme
Author: Self-Help WordPress User
Template: interface
*/

@import url("../interface/style.css");
.wrapper {
width: 95%;
background-color: #fff;
}

It will work all widgets using your child theme
If still there is problem then simply Go to Appearance -> Theme Options -> Design Options Tab -> Custom CSS and add your CSS code and Click on save all changes button:

Thank you!