ubuntu 18. use gnome-tweaks

<<install gnome-tweaks

　　sudo apt-get install gnome-tweaks

<<run gnome-tweaks

　　>>press : alt+F2 or alt+Fn+F2

　　　　gnome-tweaks

<<select window

　　set the  : 　　titlebar buttons > Placement > left or right

Installation:

1.- Extract the zip file to the themes directory i.e. ~/.themes/ or /usr/share/themes/ (create it if necessary).

2.- To set the theme in Gnome, run the following commands in Terminal.

gsettings set org.gnome.desktop.interface gtk-theme Juno 
gsettings set org.gnome.desktop.wm.preferences theme Juno 

or Change via distribution specific tweaktool.

INFO
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1. GTK+ 3.20 or later

2. GTK2 engines requirment:

(1). GTK2 engine Murrine 0.98.1.1 or later.
(2). GTK2 pixbuf engine or the gtk(2)-engines package.

Fedora/RedHat distros:
yum install gtk-murrine-engine gtk2-engines

Ubuntu/Mint/Debian distros:
sudo apt-get install gtk2-engines-murrine gtk2-engines-pixbuf

ArchLinux:
pacman -S gtk-engine-murrine gtk-engines

Other: Search for the engines in your distributions repository or install the engines from source.
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Icon theme
Arc icon theme: https://github.com/horst3180/arc-icon-theme