CSS code for a coloured border around main content area?

Can I have some help for custom CSS code to add a red border around the edges of the main content boxes and the boxes below it please?
Thank you
Gavin

 

Hello,

Paste this code in Custom CSS
Appearance > Theme Option > Styling Option > Custom CSS

Code:

.main_container{
border:3px solid red;
}
.feature-content{
border:3px solid red;
} 

Thanks & Regards
Gourav Shrivastava