UIKit Grid Element widths

I have been trying, without any success, to use the .uk-width-* class to alter the width of Grid Elements.

getuikit.com/docs/width



Where should I use this class to make the two Grid elements shown in this screenshot to equally fill the width of the available space, side-by-side?

many thanks
Matt

www.dsoxford.org.uk  

Maby, test this CSS Code:

@media (min-width: 1600px) {
.uk-child-width-1-3\@xl > * {
width: calc(150% / 3);
}
}

Hello, 
just open the Template options and insert a padding left and padding right to the section or element where the uikit grid is located