Well each theme can interpret measurements differently, especially leading which can really change the way a piece looks. Even using a percentage basis depends on what your ‘default’ setting is.
The 1-7 refers to the Heading command in HTML, with one being the biggest and 7 being the smallest, but there are no font sizes involved, so if your theme modifies <h6> to be 4pt instead of 7pt or whatever then any text which contains the <h6> command will be changed by your theme.
If I use an article it will either have no set fonts or layout, just consisting of basic text or perhaps some basic html like <p>’s in which case, your theme settings will take precedence. But if my piece has lots of format settings in it, they’ll either overrride your theme settings or your theme will override them.
Case in point: your red ribbon doesn’t like being next to a <table> command, as your red ribbon is left-aligned so text runs around it and it forces all the contents of the container over to the right.
Or for example, your Bold Hover over links only works if the text isn’t already Bold. Ideally, an already bold link should go to normal when you hover over it.