When using the Boost theme, unchecking the "Arrange content buttons horizontally" in a Lesson content page does nothing. Using the Clean theme, the buttons are then arranged vertically (pic: Lesson vertical buttons Clean theme).

To reproduce the problem:

1. Switch to Boost theme.
2. Add a Lesson activity.
3. Add a content page with multiple content buttons. Make the text for the buttons shorter than the main window width so that multiple buttons fit on one row.
4. Ensure that the "Arrange content buttons horizontally?" is checked.
5. Preview the content. At this point, the buttons should be arranged horizontally. (If the text for the buttons is long or if there are lots of buttons, then the buttons might fill multiple rows.
6. Edit the content page to uncheck the "Arrange content buttons horizontally?" box.
7. Preview the content. At this point, the buttons should be arranged vertically. What I get is that it looks exactly the same as before.
8. Add the follwoing code to the Boost Theme Raw SCSS:
   body#page-mod-lesson-view .vertical .singlebutton { display: block; margin-bottom: 0.1rem; }
   body#page-mod-lesson-view .vertical .singlebutton + .singlebutton { margin-left: 0; }
   body#page-mod-lesson-view .vertical .singlebutton .btn-secondary { min-width: 15em; }
9. Refresh the lesson page and the buttons are now arranged as they should be.