GTK Themes

GTK themes are in mate-themes under desktop-themes/. Each theme directory contains:

MyTheme/
├── index.theme.in        # theme metadata
├── gtk-2.0/              # GTK 2 CSS/assets (keep for compatibility)
├── gtk-3.0/              # GTK 3 CSS and assets  ← main work
│   ├── gtk.css
│   ├── gtk-main.css
│   ├── gtk-widgets-*.css
│   └── assets/           # PNG or SVG widget graphics
├── metacity-1/           # window border decorations
└── xfwm4/                # XFWM4 compatibility (optional)

index.theme

[Desktop Entry]
Type=X-GNOME-Metatheme
Name=MyTheme
Comment=A MATE GTK theme

[X-GNOME-Metatheme]
GtkTheme=MyTheme
MetacityTheme=MyTheme
IconTheme=menta
CursorTheme=mate
ButtonLayout=menu:minimize,maximize,close

GTK 3 CSS

GTK 3 themes are plain CSS with GTK-specific properties and selectors. Key files:

Look at Menta or GreenLaguna as well-maintained starting points. BlackMATE is a good reference for dark themes.

Testing a theme

Install the theme directory to your local themes folder and switch to it:

mkdir -p ~/.themes
cp -r MyTheme ~/.themes/

# Apply with gsettings
gsettings set org.mate.interface gtk-theme 'MyTheme'

# Or change it in the Control Center → Appearance → Theme

Use the GTK Inspector to live-edit CSS while the app is running — no restart needed:

GTK_DEBUG=interactive mate-terminal

References

• GTK 3 CSS properties
• GNOME HIG 2.2.1 — MATE’s visual design reference