Reply To: Setting the size of the featured image in the home page slider

For mobile screens you can use different styling by wrapping the CSS code with a media rule like so:

@media screen and (max-width: 768px) {
    .slide {
        background-size: 80%;
    }
}

This in addition to to previous code would make the background size 50% on screens above 768px wide, and 80% on screens below 768px wide.

Thanks for the suggestions but unfortunately that would be beyond the rules of what themes are allowed to do if they are to be included in the wordpress.org theme repository. The rules say that would be classed as content creation which is the domain of plugins.