You get around it by using a style sheet such as you can borrow or adapt from my blog at
notjohnkdp.blogspot.com
Personally, I would stay away from Calibre. I'm told it's great for people who know a lot of html and CSS, but it can bite people who don't. I would open that html file in Sigil and build an epub from it (epubs convert just fine on the KDP). There's a Sigil forum here on MobileRead.