Feature 421 block design & features
The block is a variation of feature423 that pins to the viewport on large screens while the page scrolls through it. On large screens the section heading is kept for screen readers, and the large chapter titles lead visually.
Instead of a list, the left column shows one chapter at a time: a very large faded number, the chapter title, a short paragraph and two points. As you scroll into the next chapter, the text slides up and out while the next one slides in from below.
The centre column holds a wide product screenshot that crossfades to match, with separate light and dark images. On the right, a thin vertical rail of segments marks the chapters. The active segment grows and darkens, and clicking a segment scrolls to that chapter. Under reduced motion the text swaps without sliding and the jump is instant.
Below the large breakpoint the block becomes a stacked list of chapters, each with its number, title, paragraph and screenshot.