Problem
I have one Ubuntu20 Desktop(Gnome) and I want it to be fully black and ideal. As reference, I have taken one Ubuntu20 Server and Installed openbox on it.
I hided the title bar of all the applications in OpenBox by editing the configurations in /etc/xdg/openbox/rc.xml and added
<application class="*">
<decor>no</decor>
<maximized>false</maximized>
</application>
</applications>
So that it will hide the title-bar of all the applications. Also, I am able to achieve my demand. Image shown below as example.

I want to perform the same on Gnome Desktop as well, but I don't know which config file to be edited for the same.
Currently, my Gnome Looks like this

Any help for the following is appreciated Thank you.
Well, after a few days of searching... I found the solution for my own question.
This might be not the correct way to solve it, but can be used to make things work.
How to enable extensions
Install
gnome-tweaks toolThen you can see your application on
Show Application > TweaksMethod 1 Use gnome-shell-extensions package [easiest and safest way]
Step 1 Install Gnome Shell Extention
You’ll have to reboot your system (or maybe just restart GNOME Shell by pressing
<ALT>+F2and typerand PressEnter, I don’t remember it at this point). After that, start GNOME Tweaks, and you’ll find a few extensions installed. You can just toggle the button to start using an installed extension.Step 2 Install Unite Extention
For the latest release go to
https://github.com/hardpixel/unite-shell/releasesAnd then Extract to extension folder of your home directory
Then reboot or reload your Gnome shell by
<ALT>+F2thenrandEnterMethod 2: Install GNOME Shell extensions from a web browser
GNOME project has an entire website dedicated to extensions. That’s not it. You can find, install, and manage your extensions on this website itself. No need even for GNOME Tweaks tool.
Website : https://extensions.gnome.org/
Step 1: Install browser add-on
You can simply click on the suggested add-on link by your web browser. You can install them from the link below as well:
For Google Chrome, Chromium, and Vivaldi: Chrome web store.
For Firefox: Mozilla Addons.
For Opera: Opera Addons
Step 2: Install native connector
Just installing browser add-on won’t help you. You’ll still see an error like:
“Although GNOME Shell integration extension is running, native host connector is not detected. Refer documentation for instructions about installing connector”This is because you haven’t installed the host connector yet. To do that, use this command:
Don’t worry about the ‘chrome’ prefix in the package name. It has nothing to do with Chrome. You don’t have to install a separate package for Firefox or Opera here.
Now head over to https://extensions.gnome.org/extension/1287/unite/ and Turn On the Extention.
Done It's Installed
Now go to extensions and open settings for Unite
and disable all settings like this
&
Now Close the settings and you are done!
Now Your decorators are hidden.