Based on the dark theme included with LXQt (in https://github.com/lxqt/lxqt-themes), but with the red accents changed to blue (roughly based on the blue from the KDE 5 Breeze theme), and not including the wallpaper.
Put the dark-blue folder inside ~/.local/share/lxqt/themes/ to install for your user only, or in /usr/share/lxqt/themes/ for all users.