change full width

The width in the Full Width template is based on the default size of the theme. It’s basically the Content area without the sidebar.

The Guru theme is 1200px wide. You can find the default width for the entire site around line 624 in your style.css –

.site-inner {
        max-width: 1200px;
}

So in order to change that width on the Full Width Template, you would need to add something like this –

.full-width-content .site-inner {
        max-width: 1400px;
}

This allows you to change the width on the Full Width template without affecting the other pages on the rest of the site.