Well, I've been doing my own tests and I have not found any error in my installations, I've tried with versions 18 and 19 of Ubuntu and everything has gone very well, I've installed and changed themes in SLiM, as always, and nothing has failed me. I've tried on my computers, and I've even tried it on other distros and virtual machines and I have no errors.

I don't know why it should fail you on your computer, friend, but it definitely made me think about changing the description of the installation to be more specific in the SLiM installation procedure and the configuration of the themes.

I'm sorry that I can't give you a solution, but in my tests everything went well. There was someone who also reported an error in ElementaryOS Juno, and I must be honest and I've not tried in ElementaryOS lately, but I'll do it to try to solve the problem, because the problem is not in the themes that I have done, the problem is the SLiM configuration on the desktop, because in my own tests I had no fails.

Thanks for reporting the problem, friend. - Nov 09 2019
Be careful when searching for the route, you have to use your file manager in root mode, so run the "sudo nautilus" command, when nautlilus opens then go to the route "/ usr / share / slim / themes" and place the theme file in that folder.
Then you must run the command "sudo gedit /etc/slim.conf" on the terminal and press "ctrl + f", type "current_theme", and change the name for new theme.
Let me do some tests, because on my devices it works perfectly, I have even tried on virtual machines and everything works fine, I don't know if the problem is due to your machine, but I think it can be a SLiM configuration problem. - Nov 08 2019
That's strange, does it still happen with the default SLiM themes?
Because what I do when installing SLiM is then run the command in a terminal: sudo dpkg-reconfigure slim, I select SLiM and it always works.
After that I move the theme folder to the path / user / share / slim / themes, then edit the file in /etc/slim.conf, change the name of the theme and that's it, it always works.
Try reinstalling SLiM again. - Nov 08 2019
Could you explain the problem specifically?

Because I tried it on several distros before uploading a theme.
I have tried it on Ubuntu, Debian, ParrotOS, KDE Neon, Fedora, OpenSUSE and in all of them it worked very well.
Please, be specific in the problem. - Nov 08 2019
ChromeOS GTK Theme

GTK3/4 Themes by vinceliuice 103 comments

10 the best - Nov 08 2019
ChromeOS shell theme

Gnome Shell Themes by vinceliuice 43 comments

10 the best - Oct 31 2019
Thank you! };) - Oct 18 2019
Dominus Funeral

Full Icon Themes by ju1464 31 comments

10 the best - Oct 17 2019
vitas icon theme

Full Icon Themes by zayronXIO 10 comments

Amazing, ZyronXIO!

Excellent option when choosing Deepin folders.
I think that with the dark version of the folders it would look great too, maybe you can consider adding the dark version. - Oct 04 2019
Zafiro icons

Full Icon Themes by zayronXIO 272 comments

10 the best - Oct 03 2019
vitas icon theme

Full Icon Themes by zayronXIO 10 comments

10 the best - Sep 25 2019
mcOS Mojave for Plank Dock

Plank Themes by fkorpsvart 57 comments

Thank you! Enjoy it! - Sep 25 2019
Midnight

GTK3/4 Themes by g-nome 64 comments

9 excellent - Sep 20 2019
mcOS Catalina for Plank Dock

Plank Themes by fkorpsvart 17 comments

Thank you! - Sep 18 2019
mcOS Catalina for Plank Dock

Plank Themes by fkorpsvart 17 comments

Thank you! - Sep 18 2019
OS Catalina

Full Icon Themes by zayronXIO 144 comments

Greetings, zayronXIO.

As always, it's an amazing work.

So, I tried and the Tweaks and Settings icons are still the same.

Screenshot: https://postimg.cc/Tpb9Cr7C

Again, thanks for your effort, it's awesome work. - Sep 12 2019
XONE ICONS PACK

Full Icon Themes by unc926 104 comments

10 the best - Sep 11 2019
XONE II ICON PACK

Full Icon Themes by unc926 24 comments

10 the best - Sep 11 2019
Os-Catalina-GTK-Night

GTK3/4 Themes by zayronXIO 17 comments

10 the best - Aug 18 2019
Os Catalina Gtk

GTK3/4 Themes by zayronXIO 34 comments

10 the best - Jul 28 2019
OS Catalina

Full Icon Themes by zayronXIO 144 comments

Regards ZAYRONXIO, I just installed the new update in Debian, Gnome version, and this is happening ...
https://postimg.cc/6T4g0ZV0
For the rest I have not seen anything bad, just that, excellent work. - Jul 15 2019
Modjave

GTK3/4 Themes by hunterjs 10 comments

10 the best - Jul 13 2019
Solarized Deluxe Icons and Animated Cursors

Full Icon Themes by rtl88 19 comments

9 excellent - Jul 07 2019
PearBlueDark

Full Icon Themes by adhe 9 comments

9 excellent - Jul 07 2019
OS-X Classic Version

Cairo-Dock Themes by fkorpsvart 4 comments

Thanks }:) - Jul 06 2019
OS-X Classic Version

Cairo-Dock Themes by fkorpsvart 4 comments

Thanks }:) - Jul 06 2019
mcOS Catalina 3D Version for Cairo Dock

Cairo-Dock Themes by fkorpsvart 2 comments

Thanks!! - Jun 28 2019
mcOS Mojave 3D Version for Cairo Dock

Cairo-Dock Themes by fkorpsvart 2 comments

Thanks!! - Jun 28 2019
mcOS Dock Default Colors

Cairo-Dock Themes by fkorpsvart 2 comments

Thank you, sdmf }:) - Jun 28 2019
mcOS Catalina for Telegram

Telegram Themes by fkorpsvart 6 comments

Thanks, sdmf };) - Jun 27 2019
mcOS Catalina for Cairo Dock

Cairo-Dock Themes by fkorpsvart 4 comments

Thank you!! - Jun 27 2019
Ittu motion theme 2 for SDDM

SDDM Login Themes by adhe 6 comments

10 the best - Jun 23 2019
XONE Catalina Night

Gnome Shell Themes by unc926 135 comments

10 the best - Jun 17 2019
XONE Catalina

Gnome Shell Themes by unc926 179 comments

10 the best - Jun 17 2019
OS Catalina

Full Icon Themes by zayronXIO 144 comments

10 the best
Amazing!! - Jun 14 2019
Light Glow Tubes

Plank Themes by fkorpsvart 2 comments

Thanks! - Jun 11 2019
Layan gtk theme

GTK3/4 Themes by vinceliuice 190 comments

10 the best - Jun 10 2019
Simply Circles

GTK3/4 Themes by ju1464 28 comments

10 the best - Jun 08 2019
Vimix-icon-theme

Full Icon Themes by vinceliuice 66 comments

10 the best - Jun 05 2019
Canta icon theme

Full Icon Themes by vinceliuice 9 comments

10 the best - Jun 05 2019
Cupertino iCons

Full Icon Themes by umayanga 271 comments

Awesome!!
Could you make a round icon for the Vivaldi browser? - Jun 05 2019
Cupertino iCons

Full Icon Themes by umayanga 271 comments

10 the best - Jun 05 2019
mcOS Catalina for Plank Dock

Plank Themes by fkorpsvart 17 comments

>_Thank you, @yuriygnome!!

Take a look at the Mojave version. - Jun 05 2019
Suru Plus Aspromauros

Full Icon Themes by gusreis1989 50 comments

10 the best - Jun 05 2019
Snow

GTK3/4 Themes by eliverlara 87 comments

8 great - May 18 2019
Fluent GTK Theme Set

GTK3/4 Themes by freefreeno 10 comments

9 excellent - May 18 2019
deepin plus all icon theme

Full Icon Themes by zayronXIO 22 comments

Greetings, ZAYRONXIO.

There is a small problem with the icons in Wingpanel in Pantheon.

Screenshot: https://imgur.com/a/CpTsnE1 - May 18 2019
Bibata

Cursors by Kaiz 176 comments

9 excellent - May 18 2019
Papirus

Full Icon Themes by x-varlesh-x 376 comments

10 the best - May 18 2019
Papirus Remix

Full Icon Themes by sira313 11 comments

10 the best - May 18 2019