I deleted the content.css file in the Reboot child theme and did what you initially suggested, changing the sp-content.css file.  That worked and now the default is 14px.

I don’t know what you mean by “the extra plug in I added to the editor”.  What extra plug in did I add?  Do you mean the default buttons in the toolbar of Tiny Editor?

I’m happy to stay at 14px default if it’s very difficult to make it 15px.  Let’s not make perfect the enemy of good. 

I was referring to the extra tinyMCE font selection dropdown you added…

so figured out the discrepancy here…   our themes are not actually designed by default to look for a custom content.css file…   but our child theme we use here (based on reboot), added a small piece of code that enables it…

so you can do this too if you like…  in your child theme spFunctions.php file, simply add this small piece of code:

add_filter('sph_tm_init', 'sp_myreboot_tm_init');
 function sp_myreboot_tm_init($tiny) {
 $tiny['content_css'] = SPTHEMEBASEURL.'my-reboot/styles/content.css';
 return $tiny;
}

and it will load a custom content.css for you….  note, you need to change the directory my-reboot to match your child theme directory…

and then create a content.css file and add the styles you want/need.. for example:

body {font-size: 15px;}

and voila…

It did not work.  I changed this ‘my-reboot/styles/content.css’ to this ‘reboot-child/styles/content.css’.  I copied the code to spFunctions, created content.ss and changed font to 19px.  The default font of Tiny Editor remained at 11pt.  I reverted back to what it was, the initial solution Mr. Swordfish suggested and for now the default stays at 14px.

did you use the raw code button to get the code?  if you copied from the html page, you may have gotten incorrect entities for the quotes…

Yes.  I copied the code from the pop up window that appeared and I made sure that the quotation marks are correct.

at a loss… working fine for me – would have to see it in play on your end… but sounds like you are fine where its at…