How to add a custom CSS to a shiny flex dashboard

Hi, I'm new at the shiny world.
I've done this:

---
title: 'Title'
runtime: shiny
output:
  flexdashboard::flex_dashboard:
    css:  www/a.css
  orientation: rows
---

I read that you can modified fonts, sizes and more through a CSS file. I would like to know how to apply a custom CSS. I've read that the CSS needs to be saved in a "www folder". But I don't understand what does that means. I have never posted an app, for now it's just in my computer.

The a.css file (and that is all it's name) is located in the same folder as the .Rmd file is, and have:

.chart-title {
  font-size: 48px;
}

What do I have todo to apply the efects od the CSS? and what about the "www folder"? what is that? I don't know anything about html.

Thank you!!

You have to place your a.css file in a separate www folder, which needs to be placed in the same folder as your .Rmd file.

Note: in your Rmd file you may also refer to your css file as css: a.css.

HTH

If you wish to get a better understanding on this topic, you may find this RStudio article helpful