The UI of xscreensaver window is a bit old and not so retro as it could be. Unfortunately there is no way to customize the window view mode and elements placement (except rewrite it to your needs). But there is a field for experiments with colors and sizes for some elements.

Settings file should be located in the home folder of your user:

~/.Xresources

 

I user the settings below:

 

xscreensaver.splash: false


!font settings

xscreensaver.Dialog.headingFont: -*-dina-bold-r-*-*-12-*-*-*-*-*-*-*

xscreensaver.Dialog.bodyFont: -*-dina-medium-r-*-*-12-*-*-*-*-*-*-*

xscreensaver.Dialog.labelFont: -*-dina-medium-r-*-*-12-*-*-*-*-*-*-*

xscreensaver.Dialog.unameFont: -*-dina-medium-r-*-*-12-*-*-*-*-*-*-*

xscreensaver.Dialog.buttonFont: -*-dina-bold-r-*-*-12-*-*-*-*-*-*-*

xscreensaver.Dialog.dateFont: -*-dina-medium-r-*-*-12-*-*-*-*-*-*-*

xscreensaver.passwd.passwdFont: -*-dina-bold-r-*-*-12-*-*-*-*-*-*-*


!general dialog box (affects main hostname, username, password text)

xscreensaver.Dialog.foreground: #ffffff

xscreensaver.Dialog.background: #111111

xscreensaver.Dialog.topShadowColor: #111111

xscreensaver.Dialog.bottomShadowColor: #111111

xscreensaver.Dialog.Button.foreground: #666666

xscreensaver.Dialog.Button.background: #ffffff


!username/password input box and date text colour

xscreensaver.Dialog.text.foreground: #666666

xscreensaver.Dialog.text.background: #ffffff

xscreensaver.Dialog.internalBorderWidth:24

xscreensaver.Dialog.borderWidth: 0

xscreensaver.Dialog.shadowThickness: 2


!timeout bar (background is actually determined by Dialog.text.background)

xscreensaver.passwd.thermometer.foreground: #ff0000

xscreensaver.passwd.thermometer.background: #000000

xscreensaver.passwd.thermometer.width: 8


!datestamp format--see the strftime(3) manual page for details

xscreensaver.dateFormat: %I:%M%P %a %b %d, %Y

 

More information on Arch wiki: https://wiki.archlinux.org/index.php/XScreenSaver

The picture on the left side located in the folder /usr/share/pixmaps files xscreensaver.svg and xscreensaver.xpm.
But I had no time to figure out with them.