All of the sublime settings are controlled by Preferences.sublime-settings which can accessed by going toPreferences ▸ Settings. To change fonts, you have to add font_face key to the file as follows

{
    ...
    "font_face": "Fira Code",
    ...
}

For more customisation, checkout Package Control.

Just look for plugins for it. You can change the theme colours along with fonts/font colours.

My colour highlighter theme is Monokai (SL) and my overall theme is Monokai (SL) too.

Just google sublime theme/colour plugins - you may need to install the sublime package control.