How to control font size of header in xaringan slides?

Question

I am using xaringan in rmarkdown with the following yaml heading.

---
title: "business"
subtitle: "investment"
author: "Instructor"
institute: "University"
date: "`r Sys.Date()`"
output: 
  xaringan::moon_reader:
    css: [default, metropolis, metropolis-fonts, "styles_s4.css"]
    lib_dir: libs
    nature:
      highlightStyle: arta
      highlightLines: true
      countIncrementalSlides: false
      
---
<style>
.remark-slide-content.hljs-default {
  border-top: 40px solid #23373B;
}

.remark-slide-content > h1 {
  font-size: 40px;
  margin-top: -85px;
}

</style>
---
# The Goods Market: Consumption

blah blah

---

# Remarks on Investment Decision

blah blah

But I always have a trouble squeezing my slide title on the top banner. In the following slide, I want to put "important remarks on investment decision". Any tip?