What you’re seeing is likely due to the mobile viewport and default CSS behavior. On desktop, fixed widths and margins work as expected, but on mobile, without a proper meta viewport tag or responsive CSS (@media queries), margins can behave unpredictably. Also, if the slideshow container is wider than the screen or using display: inline-block/float, margin: auto may not center as intended.

If you want a more robust solution, a responsive redesign using modern CSS (flexbox or grid) is usually the way to go. For projects like this, specialized mobile web development teams, such as Nij Web Solution, can help make sites display perfectly across devices without breaking existing layouts.