Never noticed this before, but Apple uses vertical responsive web design. As you expand your browser window vertically, the images scale accordingly. Of note are the breakpoints Apple uses. Notice they always leave a little bit of the next section visible. This is so people realize there is something below, so they scroll. If that was just solid white, you might not think anything was below this main image.
This is another example of where there is no “fold” anymore. And that people scroll, if you give them a reason to.
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