[css-overflow] Proposing `scroll-start`: allowing overflow scroll to not always start at 0 on 1st layout pass

📄 Explainer

Currently, JavaScript needs to show up at "never the right time" to adjust a scroll position to a specific starting place. This CSS property proposal seeks to remedy page load scroll jank by allow specifying a scroll-start position with a specific or by giving a child element scroll-start-target: auto at which point an absolute length is derived from the element and the scroll direction.

Example: set the start position to an absolute value:

:root { --nav-height: 100px }

.snap-scroll-y {
  scroll-start-y: var(--nav-height);
}

Example: set the start position to a snap child

.snap-scroll-inline {
  overflow-inline: scroll;
  scroll-snap-type: inline mandatory;
}

.snap-scroll-inline > #snap-start {
  scroll-start-target-inline: auto;
}

There's a lot more use cases and details (like interaction with fragment navigation) about the proposal in the Explainer

Would love to present the details of the explainer to the CSSWG for feedback 🙂

Start by reading the linked css-scroll-start Explainer and the discussion in this issue, including its fragment-navigation considerations. The proposal covers new scroll-start and scroll-start-target properties, but no specification file, test, or implementation entry point is identified. Done would require CSSWG feedback and a resolved direction for the proposal.