I am using a template for my website, namely

I wish to increase the font size of the nav bar menu item on a small screen like a mobile. Normally it works fine on a desktop screen but when the screen collapses to mobile it also works as usual but the menu font size is very small to read.
for this, I tried the code below but it didn’t work.
Note: I am using bootstrap 4

Im having trouble while trying to place the logo of my HTML page right next to the navigation bar.