I do not use this desktop theme or i3 anymore and cannot provide support for newer users who want to try it. If it works for you-- great. If you can't get it figured out, I'm sorry, but I will not be able to help you. Good luck!!!
I did it like this:
Install Vim gruvbox theme. I use the 'vim-plug' plugin manager and enable vim gruvbox theme along with 256 colors in vimrc. Source the gruvbox color sh script in .bashrc or .zshrc since I use URxvt (see my "note-about-terminals"). I installed lightline which will use the vim gruvbox theme if you set it in the lightline vim settings. I also have font-awesome powerline-fonts installed along with Hack and Fantasque Sans Mono fonts. I use Fantasque Sans Mono for the terminal and Hack for almost everything else.
Apply gruvbox color scheme to .Xresources file.
Apply i3 config colors. The colors and are located at the end of my i3/config.
Install i3blocks. https://github.com/vivien/i3blocks These blocks will not all work the same out of the box for everyone. At the least you'll probably need to set your network interface because my ethernet and wifi interface will probably be different than yours. (my ethernet is 'eno1' and wifi is 'wlp2s0'.) If you don't know what yours is, try typing 'ip link' or 'ifconfig' in the terminal and check the output. If you have trouble with a particular block not displaying, try executing the script directly to see if you may be missing a package. (E.g. ./battery) Now if a 'command not found' error appears, then you need to find out what command was not found, and what package you may need to get that command. Google is your friend here. Lastly, a few of the i3blocks scripts use their own colors by default, overriding your personal preference. I disabled this and included my version of the scripts. The only thing was changed was that the scripts no longer override color settings.
I am using prezto's https://github.com/sorin-ionescu/prezto zsh config, it's more lightweight than others that are out there and by default looks great with gruvbox.
Rofi https://github.com/DaveDavenport/rofi comes with gruvbox theme included all that is necessary is to turn it on.
Conky. https://github.com/brndnmtthws/conky It is the most ugly code I've seen since 1995. I do not guarantee it will look right for you, but it displays fine on my 1366x768 laptop screen. conkyrc is the clock/date. conkyrc2 is the process list / disk space and will need some tweaking if you do not use 3 partitions, one each for boot home and root.
Dunst notification theme is nothing fancy but I included it anyways.
Make a gruvbox gtk theme. I created a GTK theme to my preferences using oomox. https://github.com/actionless/oomox I included pictures of my settings and there is also a config file in this repo.
Apply the gtk theme and double check your fonts. I use lxappearance to set the oomox gtk theme along with gtk font. I use 'Hack' font for GTK, i3, and conky. For my terminal I use Fantasque Sans Mono because I feel like it's pretty groovy.
Note: I provide links to a lot of the projects here, but it is generally best to install them using a package manager from your distro.
And that is all.