My understanding of CSS is less than basic. I have a vague idea of what some elements do, and I manage to customize for example their colour or font size. But I really don't understand how to achieve the following.

I like very much the downcute CSS style from the rmdformats collection (here's an example).

But I prefer the position of author & date in the bottom-left corner, under the TOC, as in the readthedown CSS (here's an example).

I tried to achieve this by adding a custom CSS, copying in it some elements (for example, "#postamble") of readthedown.css that seem to achieve this. But it doesn't work – it's just beyond me.

Is what I'd like to do possible to achieve in a simple way, by adding a custom CSS on top of the downcute css, for example? I'd appreciate any suggestions, mechanical instructions, or explanations of how elements like "#postamble" or ".Content p.authors, .Content p.date" work.

(The HTML page is created from these templates in R with knitr)