Hi. Can you try to follow these steps?
- select your hader element, give it position:relative, and z-index of 1
- add a div inside that you nale "overlay" and place the content you want over the header (text, images) inside
- give this overlay div a z-index of 2, and position:absolute. Now position it with the potision buttons and arrows.
The rule here is: you want to position the overlay with absolute for it to be on top of the header and not in its flow (above or below, before or after). In order for it to be on top of the header, you need the header, which is the parent, to be positionned, so we gave it position:relative. It has no visual effect but now it's declared as the reference for any other positionned objects inside. Without this property, positonned objects inside will take an upper element as a reference, like the body.