Hmm…so my understanding of what you want to achieve is the result will have your ‘Left’ and ‘Right’ Arrow-hero elements remain within the 1200px range, but your image background (from the slider) will remain at full 100% (1440px)
Normally when we want to format the Slider component we wrap the whole slider in a div and then apply styling / setting to the div. Unfortunately, that would limit the width of your image to that div width - not the result you want.
Secondly, when working with pre-made components (namely, Slider) it is configured in such a way that doesn’t allow some customisation’s, like moving element hierarchy.
What to do?..well, as you only have 2 images in this case, you may need to create an interaction that would serve as a ‘Background Slider’ when clicking on your Right/Left arrows. The interaction could use the ‘move’ function.
Here’s the link to Webflow University Slider to get an accurate idea of the elements that make us the slider for you to create your own. Info around the 2:45min mark might be helpful for creating the imgae background.
Sorry wasn’t able to provide a more definite solution.