Add a "Float" position property to a component so it is unaffected by scrolling no matter what page properties are set.
You can already achieve this in Composer, although it's quite difficult to find in the UI and we should definitely have a tutorial about it!
1. Under Page Layout > Style > Advanced Properties, tick the box that says "stretch to ViewPort height"
2. Add whatever content you wish to scroll inside the page into a ScrollView component
3. Whatever you want to float, have *outside* of the ScrollView, and under Style > Advanced Properties, set to position: absolute. Adjust positioning from page under Style > Position tab (next to Margin/Padding tab)
@Merituuli Melkko: I followed your instructions but the "float" component still scrolls even though it is outside the scroll view.