To get started:
Open any course and open the Course Settings section
Open the CSS sub-section
Set the Enable Custom CSS For This Course toggle to ON (green)
You should then see the CSS field appear. Add your CSS code to that box alongside any other code you may have already added to it.
Customizing the logo size on the top banner:
If you have a horizontally long logo, then adjust the width like you see in the code below:
nav .relative.w-9, nav .relative.w-9 > .max-w-md.p-0, nav .relative.w-9 > .max-w-md.p-0 > .aspect-w-9.aspect-h-8 { width: 180px; height: 40px; padding: 0; }