xaringan metropolis theme slide title font size - r-markdown

Question

When using the metropolis theme in xaringan (RStudio 1.2.1070)
output:
xaringan::moon_reader:
css: [default, metropolis, metropolis-fonts]
I wish to have a smaller font for the title of each slide. If I use h1 for a slide title i.e.
---
# The title of this slide
content
it works as expected, but if I try to use h2 i.e.
---
## The title of this slide
content
the text appears in the body of the slide and not the banner.
Suggestions?
Update
Thanks for the prompt answer Martin. I modified your suggestion slightly.
Including:
.remark-slide-content.hljs-default {
border-top: 40px solid #23373B;
}
adds the border to the title slide (which I didn't want).
For me, just adding this works fine:
<style>
.remark-slide-content > h1 { font-size: 35px; margin-top: -88px; }
</style>
Nevertheless, I must say my original question about using ## was prompted by the entry on xaringan Presentations in R Markdown: The Definitive Guide https://bookdown.org/yihui/rmarkdown/xaringan-format.html where it states:
7.3.1 Slides and properties
Every new slide is created under a horizontal rule (---). The content
of the slide can be arbitrary, e.g., it does not have to have a slide
title, and if it does, the title can be of any level you prefer (#,
##, or ###).

Answer 1

Try the following:
---
title: Test
output:
xaringan::moon_reader:
css: [default, metropolis, metropolis-fonts]
---
<style>
.remark-slide-content.hljs-default {
border-top: 40px solid #23373B;
}
.remark-slide-content > h1 {
font-size: 20px;
margin-top: -55px;
}
</style>
---
# The title of this slide
content
I guess you have to play around with the settings to achieve exactly the layout you want.