To have largely all look the same application is partially engage manual demand. Applications based on gtk-1, gtk-2, gtk-qt and 3. Whereby gtk-1 hardly likely to still occur.

The following applications should be installed:

gnome-tweak-tool (applied theme to more apps than lxappearance)
lxappereance
qtconfig-qt4

To be sure, that gtk-2 and 3 have correct settings we edit the configuration files in your home directory

.gtkrc-2.0
.config/gtk-3.0/settings.ini

and make sure, that is stored there, the name of the theme and icon themes. Entries should look like this:

gtk-theme-name="Flat-Plat"
gtk-icon-theme-name="Paper"

Later this can also be done by lxapearence. We first create the file: /home/username/.gtk-2.0.mine and filled with the following content:

gtk-xft-hinting = 1
gtk-xft-hintstyle = hintfull
gtk-xft-rgba = rgb

Next, ensured that the file that is called the file by .gtkrc 2.0. For this we depend following line in the gtkrc 2.0 to:

include /home/username/.gtkrc-2.0.mine

Sometimes it is necessary, that GTK2_RC_FILES variable is exported. We add this line at the beginning of the file:

/etc/X11/xinit/xinitrc.d/40-libcanberry-gtk-module.sh

If the file does not exist the libcanberra-gtk-module must be installed. Then the following line is inserted.

export GTK2_RC_FILES="$HOME/.gtkrc-2.0"

Now the GTK Themes for all GTK applications should also be possible using gnome-tweak-tool or lxappereance. To provide the QT apps with the same theme, QT Settings are called with qtconfig-qt4. There you will about the gui style on GTK. Now, the design should look consistent and nicely.