The major difference is the new shell replacement for gnome-panel, that is gnome-shell. GNOME Shell + Mutter brings the whole new experience for user interactivity. Unlike gnome-panel which is very limited in customization if you are not familiar with programming. gnome-shell is designed from ground-up with CSS and JS technology built-in. Every components of the shell are visible and customizable.

Yes, it is possible.
Just change the /usr/share/gnome-shell/theme/gnome-shell.css accordingly.
For example, if you want to change panel font, you can add font-family: “FontName” into .panel-button.
And you can further customize the font of the Dashboard, etc.

After this you have to restart gnome-shell: press Alt+F2, type “r” (without quotation marks), and press Enter.

CSS is located under /usr/share/gnome-shell/theme/gnome-shell.css
JS for UI is located under /usr/share/gnome-shell/js/ui/

You can change pretty much everything of the gnome shell.
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