Thats correct add it to the very bottom of the stack as standard, if it doesn’t work try adding it to the top of the stack which would suggest that there is some broken CSS in your stack. If some CSS is not written correctly, any CSS below it may not work.
I suggest that you choose either Simple CSS or Additional CSS to add all of your CSS too – don’t split it between the two.
Simple rule with CSS – it stands for Cascading Style Sheets. So if there are two CSS rules the one below it will overwrite the one above it eg.
.mobile-header-navigation .site-logo.mobile-header-logo img {
height: 80px;
}
Followed by:
.mobile-header-navigation .site-logo.mobile-header-logo img {
height: 180px;
}
The second one will overwrite the first.