Positioning of buttons from top (.annotator-frame div)

## Bug report form
### Steps to reproduce

I'd like the functionality to be able to edit the position of the .annotator-frame div from the top. I'm able to do it with CSS just now, but it woudl be good to have this built in (I've been chatting to Robert Knight on Slack and he told me to put this forward, even though I've managed ot hack it. He says that the CSS classes could change at any time).

### Expected behaviour

I want the annotator frame div to have a bit of space form the top of the page, so it doesn't block out my learning template info button.

### Actual behaviour
Currently working, but hacked, and may not be futureproof.

### Browser/system information
all

### Additional details

## Feature Request Form
### Problem you are trying to address with this feature

### Your solution

Be good to have it as one of the options.

### Add tags - did you add labels?
If this a customer requested feature, make sure to add that label.

The issue identifies the .annotator-frame div as the entry point; inspect the frontend code that creates and positions it and determine how configuration options are exposed. Define the supported top spacing and verify that it works without a CSS override while preserving the existing layout behavior.

Written by the indexing model from the issue text.