I was searching everywhere for this, but I was wondering if there is a way to install the new Yaru theme on Lubuntu 18.10, without having to build from source?
I was thinking that I could simply install the Communitheme snap that I found on Discover (the Lubuntu software center), but I didn't know what to do next.
I know that Yaru is a GTK theme as well, so I thought it would be easy to just install the Communitheme snap, but I'm not sure.
Thank you in advance!
As per the attached screenshot, I realize that Lubuntu can work with GTK themes, but I'm a little confused as to how to do this...
EDIT 2:
I used the terminal to install the Snap version of Communitheme and did not get any errors. However, I do not know how to choose the Communitheme session; the only options when selecting the gear at the upper left corner of the screenshot above are "Lubuntu Session," "LXQt Desktop Session," and "Openbox Session."
You should be able to install the Yaru theme in Lubuntu 18.10
Unlike 18.04 which used LXDE, Lubuntu 18.10 has a Qt desktop, LXQt. That means that, like in Plasma/KDE (which I'm using right now myself, although I have used LXQt untill recently), the GTK themes like Yaru will not cover most of your desktop, but only the appearance of applications that have a GTK gui, like Firefox, Deadbeef, Audacious, Disks, uGet, etc.
If that is what you want, install Yaru as said above and enable it for both GTK2 and GTK3 from settings in your first posted image.
The other parts in the appearance of the LXQt desktop are:
the Qt-styles: covering the full texture of all Qt applications (especially the file manager, and specifically setting the light or dark look ) - more about that here.
the LXQt theme: covering mostly the panel
the Openbox settings: covering windows
the icons
Unlike in Plasma settings, in LXQt settings there is no option for icons in GTK applications, as you can see. I think what happens is that GTK apps will use the main icon set.
Yaru package includes a dark theme only for its GTK3 version though, which might be a problem if you use a dark qt-style (like Breeze Dark, or Kvantum Dark) with icons adapted to those (that is: light icons): the GTK2 apps will have light theme with light icons. So, if you chose Yaru theme you should EITHER avoid using dark Qt-styles OR GTK2 applications.
In Plasma 5 there is an option for GTK themes where you can chose "prefer dark GTK3 theme", which then makes the gtk2 apps use a dark theme too. But that option seems absent in LXQt.
There are other good GTK themes both dark and light that can be installed in LXQt, the problem with GTK theming in a Qt desktop is one of integration.
The most obvious good integration of GTK application in a Qt desktop these days is provided by the Breeze qt-styles with the Breeze GTK themes. As you already use the Breeze qt-style, you can use the Breeze GTK package too, which has light and dark themes both for GTK 2 and 3.