I assume the title part is fixed and the slides are sliding underneath it.
You have to carefully chose where you put the elements that will get your overlay content. It can’t be, obviously, inside of the Slide element, but rather just under the Slider element.
I made the triangle by rotating a div but there’s tons of options for this. I’d make a SVG triangle, it’s easier. What’s cool with the rotated div is that you can animate its position and rotation with IX.