/usr/share/themes/Synthetic/xfwm4/themerc is in xfwm4-themes 4.10.0-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | active_text_color=#FFFFFF
active_text_shadow_color=#264C73
button_offset=1
button_spacing=0
full_width_title=false
title_horizontal_offset=2
title_shadow_active=true
title_shadow_inactive=false
title_vertical_offset_active=2
title_vertical_offset_inactive=2
|