CSS in a markdown cell to change the font size?

Hello,

This is probably all over the place. I would like o change the font size (and colour and see whether @font-face can work in a Notebook markdown cell, but let’s start slow). I don’t really know what I am doing and only found this in a 2013 video you can see here. The relevant (maybe not) bit is at 22:40.

He uses the following code in a markdown cell:

<style>
    body {
        font-size: 20px;
    }
</style>

He then has an unrelated HTML call in which he only uses header tags anyway, so I am not sure where this CSS is supposed to act, but he does say the purpose of the CSS in the Markdown cell is to increase the font size for the whole notebook but leaves images alone (as opposed to CTRL+ to zoom in, which increases the whole display). This intent is to make the Notebook more readable in a presentation (the presentation he has just given).

When I try it, the CSS does not increase the font of further Markdown cells or text in further HTML code. I am certain I am doing something wrong but this is a 2013 IPython pres and I really have no idea how to approach the subject using the latest Jupyter Notebook (Anaconda install).

The bottom line is that:

I would like to increase the font size for the whole notebook or, if I can do that, only for some portions of Markdown cells.
I do not want to mess with the CSS file that governs ALL notebooks. I only want to try and find a way to increase font size for some Notebooks or portions thereof.

Is this possible?

Thank you for your comments and suggestions.

All the best. C