A GTK theme based on the colours of Sainnhe's great theme: Gruvbox Material for Neovim, the VinceLiuice's awesome: Magnetic GTK theme and the creativity of Ggusbemacbe's: Suru Plus Icon Theme.
Great to combine in your Gnome Desktop Environment and TWMs like: XmonadWM, AwesomeWM, BSPWM, etc... With support also for the desktop environments Cinnamon and XFCE.
You can check Reddit: r/unixporn to get some ideas.

Before installing, make sure to install the Murrine Engine and gnome-themes-extra packages for the correct rendering of themes.

Here are some commands to install on some distributions.

• On Fedora run:

 sudo dnf install gtk-murrine-engine

• On OpenSUSE run:

 sudo zypper install gtk2-engine-murrine

• On Arch run:

sudo pacman -S gtk-engine-murrine

• On Debian and derivatives run:

sudo apt install gtk2-engines-murrine

The themes work on versions 40 to 44 of the GNOME D.E. just follow the steps below for installation:

• Download the themes packs and extract them
• Move the extracted files to the following paths:
  • For GTK3: ~/.themes In this path you must move the entire theme folder.
  • For GTK4: ~/.config/gtk-4.0 The files to move to this path can be found inside the theme directory in the gtk-4.0 folder, copy only the assets, gtk.css and gtk-dark.css files or create a symlinks.

• For GTK3, apply themes from Gnome Tweaks.
• For GTK4 applications it is only necessary to have moved the assets, gtk.css and gtk-dark.css files to the ~/.config/gtk-4.0 path, and if you notice that the theme has not been applied, just close and reopen the application.

• Override flatpak themes to ~/.themes:

sudo flatpak override --filesystem=$HOME/.themes

• Override flatpak icons to ~/.icons:

sudo flatpak override --filesystem=$HOME/.icons

• Override flatpak themes to ~/.config/gtk-4.0 locally:

flatpak override --user --filesystem=xdg-config/gtk-4.0

• Override flatpak themes to ~/.config/gtk-4.0 globally:

sudo flatpak override --filesystem=xdg-config/gtk-4.0

Base theme default instructions

Run the following commands in the terminal:

./install.sh

Tip: ./install.sh allows the following options:

-d, --dest DIR          Specify destination directory (Default: ~/.themes)
-n, --name NAME         Specify theme name (Default: Tokyonight)
-t, --theme VARIANT...  Specify theme color variant(s) [default|purple|pink|red|orange|yellow|green|teal|grey|all] (Default: blue)
-c, --color VARIANT...  Specify color variant(s) [standard|light|dark] (Default: All variants)
-s, --size VARIANT...   Specify size variant [standard|compact] (Default: standard variant)

-l, --libadwaita        Link installed gtk-4.0 theme to config folder for all libadwaita app use this theme

-r, --remove,
-u, --uninstall         Uninstall/Remove installed themes or links

--tweaks                Specify versions for tweaks
                        1. [moon|storm]        Moon|Storm| ColorSchemes version
                        2. black                    Blackness color version
                        3. float                    Floating gnome-shell panel style
                        4. outline                  Windows with 2px outline style

-h, --help              Show help

For more information, run: ./install.sh --help

This is just to clarify doubts about the abbreviations of the Themes, as many found the names confusing.

Thanks to @f1yn for the solution to the active and inactive borders in the new version of Cinnamon which no longer uses Metacity.

Thanks to @telometto for the alternative for the application of themes in Flatpak.