Thanks for that, @spektukal! So there's a couple things going on here, hopefully I can help explain everything clearly and point you all in the right direction on this.
As for the header appearing to cover content (both with the intro image and the sections as you click the links and it auto-scrolls), everything is working as it should. As you can see from this screenshot here showing an overlay of where your content starts after the header, you'll see it starts right below the header:
The reason why the image here appears to be "cut off" as you mentioned simply has to do with the CSS being used to make the image span the entire dimensions of your section. By default, the advanced background images used in the theme use
background-size: cover in CSS, which effectively does what it sounds like it should do: ensure that the image should cover all available space of the parent section it's in. Alternately, if we were to use something like
contain as a CSS value, you can see the actual dimensions of the image used:
So we can see in this example the image is "contained" by the section, which keeps the image's actual proportions, showing us that we're using more of a "portrait" orientation here rather than "landscape" to match the section layout. However, just cropping your image to landscape does not ensure that all parts of a background image will be visible at all times on all devices at all breakpoints. When using
cover for actual photos used as background images (which is what is used 99% of the time for photos as background images), you cannot ever expect the entirety of the image to be seen at any given time. The image will constantly be grown or shrunk to ensure that it is covering the whole section properly. Background images should be thought of as more decorative elements, not actual content. You can't expect to always see the whole thing, so you need to be okay with it moving and shifting to fit its container. The best you can do to see more of the image in the way you want is crop it down to more of landscape orientation, which will mean it doesn't have to grow as much horizontally and "cut off" as much of the top and bottom, but remember that the image will constantly be growing and shrinking in this configuration, it is simply the natural behavior of such a setup.