center dock icons ubuntu
First Install dconf-editor
$ sudo apt install dconf-editor
Then
$ gsettings set org.gnome.shell.extensions.dash-to-dock extend-height false
$ gsettings set org.gnome.shell.extensions.dash-to-dock dock-position BOTTOM
$ gsettings set org.gnome.shell.extensions.dash-to-dock transparency-mode FIXED
$ gsettings set org.gnome.shell.extensions.dash-to-dock dash-max-icon-size 64
$ gsettings set org.gnome.shell.extensions.dash-to-dock unity-backlit-items true