HMTL5 queries

Hi all,

So we've produced a course and need to publish to HTML5. We're aware of the limitations of HTML5, however we have encountered a few unexpected anomalies.

Firstly, lightboxes are acting up. They appear larger than expected and the content within them is even larger and extending off the page. Also the 'x' close button does not work all of the time. 

Secondly, text appears to have been re sized and re positioned.

Thirdly, when clicking a button intended to launch a new slide in a lightbox occasionally an unexpected slide is launched in the lightbox instead. This isn't a case of overlapping clickable areas (I've checked).

So my question really is....how do I go about fixing these issues without affecting the HTML version (which is working fine) and what is best practice for testing the HTML5 once changes have been mande.

Any help at all would be greatly appreciated.