Just minimal CSS, no scripting language.

Using the latest CSS techniques to have a scrolling panel snap to each element and have the content centered within the scroll window.

Photos can be any size, any orientation and any number, with the only addition to the CSS being the background image url. The only change to the html being the additional 'pics' divs.

For touch screens just swipe left and right to move between slides. The scrollbar will indicate the position of the scrolling element.

For mouse use just hover the mouse over the slideshow and use the mousewheel to horizontal scroll through the slides. The vertical movement of the mousewheel will control the horizontal movement of the slides.

The only 'problem' browser is Edge which does not correctly show the scrollbar movement when using the mousewheel so the scrollbar has been removed when using a mouse on the Egde browser.

The mousewheel horizontal scrolling is also just CSS with no javascript or jQuery.