/usr/share/themes/Albatross/gtk-3.0/settings.ini is in shimmer-themes 1.3.0-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [Settings]
gtk-color-scheme = "base_color:#ffffff\nbg_color:#EDEDED\ntooltip_bg_color:#D6DCE4\nselected_bg_color:#A9B7C4\ntext_color:#444\nfg_color:#202020\ntooltip_fg_color:#222222\nselected_fg_color:#333333\nlink_color:#4d75bf\nbg_color_dark:#303334\nfg_color_dark:#efffff"
gtk-auto-mnemonics = 1
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