HTML font attributes override styling, rather than add to it

I'm finding this problem with QML Text objects, using RichText format, but it may also apply to Qt QTextDocument objects.

If I apply a style to something like a paragraph, and then apply some font-related format to something inside the paragraph, it overrides the entire style, instead of adding to it.

For instance {{<p style="font-size: 10px">This has <i>italics</i> in it</p> }}should display everything in very tiny type, with one word italicized. Instead, the italicized word reverts to the normal text size. This happens any time formatting is applied to a portion of an element, including by a "style" attribute, or a CSS class name. This is not how web browsers work.