title: Is REM rendered based on a default font-size of the default browser/OS font, custom served font or actually fixed pixel?
body: <p>Example, considering the default of the root element defined as 16 for chrome, loading a page with Segoe UI will 1 rem be the 16px size based on Segoe body? What if the font served is something else such as Inter UI? or is REM
  it actually 16 pixels no matter which font, OS or browser? I took a screenshot of bootstrap 4 page <a href="https://getbootstrap.com/docs/4.0/content/reboot/" rel="nofollow noreferrer">https://getbootstrap.com/docs/4.0/content/reboot/</a> and measured the font which is defined as 1em and I know it's loading Segoe UI and I came up with 16pixels</p>
  
  <p><a href="https://i.stack.imgur.com/N1FtH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/N1FtH.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/Mlzve.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Mlzve.png" alt="enter image description here"></a></p>