The GNOME Project is a free and open source desktop and computing platform for open platforms like Linux that strives to be an easy and elegant way to use your computer. GNOME software is developed openly and ethically by both individual contributors and corporate partners, and is distributed under the GNU General Public License.
That's what I thought when I heard Gnome supports custom CSS: that I could customize its looks with many properties like a webpage. I did a bunch of searches about how to inspect gnome elements and you use Looking Glass, but its not quite like browser dev tools which show the whole DOM like this and with a CSS editor. I stopped since it seemed like a lot of work.
There's a good modern ricing solution for Gnome that's as close as I think you'll get... Open Bar? I don't have my gnome box on me but I think that's it. Nowhere like inspector, but I believe it supports arbitrary css changes to Gnome assuming you already known what it's named. Remember tho... Gnome is for seamless mac mouse gestures and LOVES to break ricing and watch us cry by breaking customizations on upgrades. If you want to rice, choose life, choose KDE... (I say this as a Gnome addict for real workflows)
Yeah I chose KDE and am pretty happy with it so far.