LXQt apps do not respect chosen theme


It seems none of the LXQt apps respect the theme chosen by the user, at least by me. I have and need [1] a dark background, which is respected by various apps I installed, but not by LXQt ones (including the file manager, pcmanfm-qt). Is there a way to have the theme respected?

Also, can we get other themes (there is only 1 dark theme by me).

Thank you!

[1] Really, my eyes hurt quickly otherwise; I could not read PDFs more than a few minutes before pdf readers allowed inverting colors (they should only invert luminosity…). The reason, if you want it, is that my eyes are more sensitive to light than many, and a screen, unlike a paper, is a source of light (it hurts you as well, just less or more slowly). By the way, does someone know how to do that: in Firefox, I set a non-white background (ochre) just to be able to read more than 3 min. However, some web designers (wrongly) use background images as links, buttons, or for feedback: they are then invisible for me, and I need to disable my color choice to deal with them.

You haven’t said what release of Lubuntu you are talking about. I’ll assume 19.10 for now, but please specify.

If you go into LXQt Appearance Settings, can you please note and provide the following :-

Widget Styles: (I suspect it’s here you’re issue is)
Qt Style: ?
GTK 2 Theme: ?
GTK 3 Theme: ?
Icon Themes: (If an issue)
LXQt Theme: ? (I suspect you mean Widget style using LXQt terminology, but this too if it’s your issue please)

(see https://manual.lubuntu.me/stable/3/3.2/3.2.2/appearance.html?highlight=appearance)

If you have changed colors (colours) using the Theme Configuration, and it’s these that aren’t being honored, please note it.

And please list which applications you are talking about. (This is most important!)

I suspect you’re being confused by the toolkits (GTK+ or Qt) which use different themes, so changing a GTK+3 theme may not have any impact on Qt apps, let alone GTK+2 app, and why there are multiple theme settings.

The applications are necessary, as for example Firefox (https://packages.ubuntu.com/eoan/firefox) uses the GTK+3 theme which is different to programs like pcmanfm-qt which obeys the Qt setting.

Note: I’m not a developer, so my understanding of this is very limited. Also I’m somewhat aesthetically challenged, and happily use older GTK+2, modern GTK+3 apps along with native Qt apps with different themes & don’t even notice. LXQt uses Qt5

I included the packages.ubuntu.com link for firefox as I used it to check which toolkit/theme firefox actually uses; it shows libgtk-3-0 as a dependency, ie. it must be installed for firefox to install & operate, this is what told me the program uses GTK+3 (or GTK 3) theming.

Yes, I did not give enough details, sorry.
Lubuntu 19.10

In LXQt appearance settings:

  • I changed the theme to “Dark”.
  • Qt style is Breeze, GTK 2/3 is adwaita-dark
  • Icon theme, don’t know (seems to be a bug, since none is highlighted before I click). Clicked on Oxygen, now it’s highlighted when I come back.

I have not stepped on any Theme Configuration.

I have more expensively tried various apps:

  • Most LXQt apps seem to ignore a dark theme, including most setting apps, pcmanfm, discover… I just found a few that do respect it, including alternative and screensaver (both config apps).
  • Most non-LXQt apps I have tried respect it, including FF, TB, geany (prog editor, built on gtk+ IIRC), pinta (drawing). But “noble notes” and Featherpad don’t!

As far as I know, GUI apps built on whatever GUi framework (qt, gtk, even tk now) do or at least can respect the “system” theme (as in “use system colors/fonts”). The system theme is in fact the one defined by the window/desktop system, further configurated by user parameters; as opposed to a custom style of the framework (as used to be for tk). Hope I’m clear.

Thank you for your help!

I’ll aim to return & read more tomorrow, I didn’t consider in my prior post, different ways we can get apps now.

Snaps, flatpaks & app-images can have their themes enclosed within the package & may ignore global themes.

I replied earlier today to another user (https://discourse.lubuntu.me/t/panel-doesnt-stay-on-top-of-all-applications/605/2) where I looked up bug-reports on app-images ignoring user (global) settings for icons, but it was closed as the icon set is whatever packager encloses. I’ve seen snap users complain of that too (though classic confinement I believe can get around that issue).

This is only a thought.

I also don’t have ‘Dark’, nor see it at https://www.gnome-look.org/browse/cat/446/page/1/ord/latest/ (or the other pages they there), however is it https://lxqt.org/screenshots/dark/ ?

You are only modifying GTK themes, QT themes are a bit of confusing. Easiest way to get a QT dark theme is to install kvantum (sudo apt install qt5-style-kvantum) and chose a dark theme there. Let us now how it work.
I forgot, after chosing the theme in kvantum, you will need to change the “Qt-style” for the kvantum one.

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You are only modifying GTK themes, QT themes are a bit of confusing. Easiest way to get a QT dark theme is to install kvantum (sudo apt install qt5-style-kvantum) and chose a dark theme there. Let us now how it work.

Thank you! I did it and it works fine. Now, it seems (I have not tried each and all) al LXQt apps respect my theme.

Kvantum is simply great. It’s interface is not obvious because definitely not mainstream, but it ‘‘just makes sense’’: there are 4 main sections, which unfold when clicked on, mirroring 4 usage stages: install themes, change them, configure, configure per app(s). the only faulty points:

  • Terrible, probably most mechanical, translations (had to switch to english to understand a bit ;-)).
  • Not a word about where/how to get other themes, while the feature is implemented (one can define a custom theme folder), probably related to below:
  • Help unavailable (nothing happens when clicking the button), even in english.

EDIT: Help seems to have the form of a “what’s this” pointer that should act when placed on an interface element that has help. But it only shows a tooltip that we already have by default anyway.

For the record, I found a great dark theme among the ones that come with Kvantum: KvDarkRed (modified).

I forgot, after choosing the theme in kvantum, you will need to change the “Qt-style” for the kvantum one.

So, I had to find haw to activate the chosen Kvantum them as well: LXQt setting => appearance => widget style “kvantum” or “kvantum-dark” (no difference by me). PS: see also last paragraph below.


I would argue that there is far too much confusion about styling/theming. However, most linux distribs are equally confusing. In particular, here in Lubuntu, it is totally counter-intuitive that setting a theme in LXQt setting => appearance => “LXQT theme” does ‘’’’‘not’’’’’ set a theme for Qt apps, firstly the ones of LXQt itself, isn’t it? (Orally, I would say: what the f*ck!!!)

Most if not all also are based on an underlying software windowing framework which has its own styling/theming configuration that come with its own styling/theming config, that the desktop environment transfers as is to users. Instead of integrating it into meaningful, coherent whole… After all, there is only visual theme/style ultimately :wink: . With Lubuntu we thus have the whole --BlackBox-- OpenBox config, that mostly covers the same points as the LXQt one. By the way, I also set “KvDarkRed” as theme in the OpenBox config, don’t know if I had to do it… Precisely the confusion I am talking about.

PS: The interface for posting on this forum is pretty annoying with its tiny edit and preview windows. I am also a little surprise the spellchecker underlines “english” :wink: .

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