Bug: Focus on open gets applied to hidden elements.

[davejtoews]

When opening a modal, focus is applied to the first focusable element w/in the modal. If the first focusable element is set to display: none or otherwise hidden w/ CSS, it will attempt but fail to set focus to that element and instead apply it to the modal itself. Ideally Modal.setFocusToFirstNode() would check for visibility.

[dkniffin]

@davejtoews can you please provide a codepen that demonstrates this? Here's a template you can base it on: Codepen example