The "thin blue line" in SparkeApp website construction
(NOT the riot control police !)
To see if it is there - tap Tab and scroll.
If NOT either you never inserted it OR it got lost. Recreate it.
What is it? An optional view in GRAY of an Anchor Point on the html page.
(technically it's an example of a canvas overlay)
Why have it? So you can pre-test where a button may link to.
And adjust as required (during page construction ONLY).
Testing the function.
Insert a visible (toggle option) anchor point on the page.
Scroll to view it on the page.
Test it by installing a button elsewhere, with a "Go to position on this page" option.
Really test it by clicking the button.
If it tests out..
Toggle again to make the Anchor Point, invisible, but working on the Published page.
An example result on this website = foreRunner page/the "Go to bottom" button.