The following properties have auto as their initial value, but their grammars only accept <length> values:

• scroll-padding-block
• scroll-padding-block-end
• scroll-padding-block-start
• scroll-padding-inline
• scroll-padding-inline-end
• scroll-padding-inline-start

https://drafts.csswg.org/css-scroll-snap-1/#padding-longhands-logical