I updated to the current bootstrap and did some tests. I added two rules to the end of your userstyle.css file:
h1 { font-style: italic !important; }
h2 { color: #FFA500 !important; }
The result is here.
In other words, it accepted my two rules but rejected yours.
When applying the same css to the dokuwiki template, I get the following:
Here it is a combination of your css with my additions. But there is something skewed here, because the
header 3 is shifted to the right, and I don't think that is what you intended. So I suspect there is something in your css which is not correct and/or conflicts with the bootstrap css.