Hovering over a line causes rendering issues / jumping

[lambdageek]

Because we use a :hover to display a CSS content for the bookmark pin icon, going from invisible to hover state causes a rendering jump.

Options:

1. Reserve some space in the non-hover case. (easy)
2. Redo the UX. Make the lines selectable and display toolbar buttons to bookmark/unbookmark/show long lines
3. Find a good tree-structured virtual table widget in pure HTML/CSS/JS and use it for rendering; add the bookmark icon to a column or a hamburger menu or something.