How to increase slider scroll length?

Question

css

I am making a mobile version for the site, on the main page there is a news block in the form of a slider. For the test, I put 4 entries there to look at the scrolling. The problem is that at a resolution of 768px, the slider does not scroll the records. When inspecting, I found a changeable parameter, after clicking on the "next" button, margin-left occurs: -259px. I would like to change this number, but how to write everything correctly and to which element?