Black Gorilla Theme

A pure black, high contrast GTK3 and GTK4 theme, built for cheap screens and tired eyes.

Built for the people every other tool prices out: kids with no credit card, 15-year-old laptops, data sold by the megabyte. Free forever, by design, not as a trial. Why, with the numbers: PHILOSOPHY.md

Two small CSS files that make dark-theme text actually readable. No root, no package to install, nothing outside your home folder, one command to undo.

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📸 Screenshots (Click for Full Resolution)

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🧸 Section A — For the Layman

The problem

Open any dark-themed GNOME app and look at the small grey text under a heading — a setting's description, a caption, a greyed-out menu item, or a right-click context menu on a black background. On an older laptop screen, or at night, or if you're over about forty, it's a strain to read.

That isn't your eyes. It's measurable. Here is what the standard dark theme actually draws, measured as a contrast ratio (higher is easier to read; the accessibility guidelines call 4.5 the minimum for body text and 7.0 the comfortable target):

What you're reading	Contrast	Verdict
A heading	13.20:1	fine
The small grey description text	5.17:1	just past the legal minimum
A greyed-out menu item	4.58:1	0.08 above the minimum
Context menu borders on dark background	None	invisible floating menu

Those pass the test by a whisker. Passing a test and being comfortable to read are not the same thing.

What this does

What you're reading	Before	After
Normal text	13.20:1	16.75:1
Small description text	5.17:1	8.55:1
Greyed-out items	4.58:1	6.54:1
Context menus & popovers	No border	Crisp 1px cyan border

Deep black background, bright cyan text, pink highlights, and crisp cyan borders around floating menus and popovers so they stand out clearly against the folder view. It also uses the right size of typeface for each job — more on that below — which is the other half of why text looks crisp rather than fuzzy.

Install

The easy way — download the .deb, double-click it. Nothing else to do: it applies immediately for you, and at first login for anyone else who uses the machine. On Debian, Ubuntu, Mint and Pop!_OS you can also install it from a terminal:

sudo apt install ./black-gorilla-theme_26.08.15-08-17_all.deb

The no-package way, if you'd rather not install anything system-wide, or you're not on a Debian-based system:

./install.sh           # colours only
./install.sh --fonts   # colours + set the desktop font and size

This changes every GTK application on your desktop, not one app. That's the point — but you should know it before you run it. Undo everything, including the font settings, with:

black-gorilla-theme --revert     # if you installed the .deb
./install.sh --revert            # if you ran the script

Your choice is remembered. If you revert, the package will not put it back at your next login. Removing the package (sudo apt remove black-gorilla-theme) cleans it out of every account it touched, and leaves any other CSS you had in those files alone.

Then restart an app (or log out and back in) to see the change.

Build the .deb yourself

./build-deb.sh

Produces dist/black-gorilla-theme_26.08.15-08-17_all.deb, about 16 KB. No build dependencies beyond dpkg-deb — it is shell and CSS.

Will it work on my computer?

If you run Linux with a GNOME-style desktop — Debian, Ubuntu, Fedora, Mint, Pop!_OS, Arch — yes. It needs no special hardware and no fast machine. It was built on a 2012 laptop and deliberately avoids anything that costs the graphics chip work, so it does not shorten your battery life.

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💻 Section B — For the Developer

How it works, and why it has no gaps

Two files, read automatically by GTK and loaded after the active theme, so their definitions win:

~/.config/gtk-4.0/gtk.css   GTK4 / libadwaita applications
~/.config/gtk-3.0/gtk.css   GTK3 applications (yelp, older apps)

The theme does not restyle widgets. It redefines the named colours the toolkit already uses everywhere:

@define-color window_bg_color #000000;
@define-color view_bg_color   #000000;
@define-color card_bg_color   #000000;
@define-color accent_color    #FFC0CB;

Every GTK/libadwaita widget derives its colour from that small fixed vocabulary (window_bg_color, view_fg_color, headerbar_bg_color, accent_color, borders, …). Redefine a name and every widget referencing it changes at once — including widgets added in future toolkit versions.

This is why the whole theme is ~25 declarations rather than thousands, and why it has no gaps. The usual approach — chasing selectors (button {}, headerbar {}, .sidebar {}) — cannot enumerate every widget, so there is always an unstyled popover or an invisible disabled item, and a class rename in the next release breaks whatever was covered. You cannot miss a widget you never addressed.

Explicit selectors are used only where a colour name cannot express the rule: focus rings, disabled-item visibility, context menu edges (popover > contents), edge drawing, animation timing.

Typography — optical sizes

Segoe UI Variable ships three faces cut for different size ranges:

Family	Drawn for	Used here for
…Static Small	very small text	captions
…Static Text	body / UI text	everything by default
…Static Display	large text	headings, titles

Using the right one per role is most of what makes UI text look crisp instead of muddy.

Getting the fonts, the honest way. Microsoft's EULA licenses use, not redistribution — so this repo ships the method, never the binaries (.gitignore blocks *.ttf/*.ttc). Run:

./get-microsoft-fonts.sh

It pulls the fonts from Microsoft's own free Windows 11 Enterprise 90-day evaluation download, on your machine, and installs them. Nothing is pirated and nothing proprietary is redistributed by this repo. Method credit: Arch Linux's ttf-ms-win11-auto.

You do not have to run it. font-family is a fallback list, so the theme works on any machine either way:

font-family: "Segoe UI Variable Static Text", "Segoe UI", Inter,
             Cantarell, "Noto Sans", "DejaVu Sans", sans-serif;

Segoe is used if the machine has it; otherwise the best available free face is, automatically. Nothing to detect, nothing to break.

Design rules

• Outline, never border (except popovers). A border changes box geometry and forces a CPU reflow on every focus change; an outline is drawn outside layout and composited by the GPU. Popovers use border because GTK's arrow node reads border-bottom-width to align with the panel.
• box-shadow: none on focus and popovers. libadwaita's stock focus ring and popover shadow are translucent shadows — that is exactly what makes them look faded on dark backgrounds. They are removed, not tinted.
• Dim by hue, not by alpha. Secondary text is #00B8B8 (8.55:1), not white at 55% opacity (5.17:1). Transparency over black is what produces mud.
• Animations neutralised to 0.01ms. A styled desktop should not cost the graphics chip work. This matters on pre-2016 integrated GPUs.

Verify any colour before shipping it

python3 - <<'EOF'
def L(c):
    f=lambda v:(v/255)/12.92 if v/255<=0.03928 else (((v/255)+0.055)/1.055)**2.4
    return 0.2126*f(c[0])+0.7152*f(c[1])+0.0722*f(c[2])
fg,bg=(0,255,255),(0,0,0)
print(round((max(L(fg),L(bg))+0.05)/(min(L(fg),L(bg))+0.05),2), ":1")
EOF

AA needs 4.5, AAA needs 7.0. Do not eyeball it — the whole reason the stock theme is uncomfortable is that 4.58 and 8.64 look similar in a mockup and feel nothing alike after an hour.

Files

File	Purpose
install.sh	apply / --fonts / --revert / --check. Idempotent.
~/.config/black-gorilla-theme.state	previous font settings, for --revert

Why this isn't a theme you select in Settings

Because that would not work, and the reason is measurable rather than a matter of opinion. Traced with strace on GTK 4.18.6 / libadwaita 1.7.6:

Application kind	Stylesheets it actually opens
Plain GTK4	~/.config/gtk-4.0/gtk.css and /usr/share/themes/<Name>/gtk-4.18/gtk.css
libadwaita	~/.config/gtk-4.0/gtk.css — and nothing else. It never stats /usr/share/themes at all.

Files, Settings, Software, Text Editor, Epiphany — everything modern in GNOME is libadwaita. So a theme packaged the conventional way would install cleanly, show up in tweak tools, and change nothing you actually look at. The per-user file is not a shortcut taken to save effort; it is the only mechanism libadwaita honours.

Reproduce it yourself:

strace -f -e trace=openat -o /tmp/gtk.strace gnome-text-editor & sleep 3; kill %1; grep -o '"[^"]*gtk.css"' /tmp/gtk.strace | sort -u

That is also why the .deb writes into home directories, which Debian policy normally discourages. It is bounded: only accounts carrying this theme's own stamp file are ever touched, and removing the package strips exactly the block it added and nothing else.

Known limitations

• Electron and Qt apps are unaffected — they do not use GTK's theme.
• Some apps hardcode colours and will ignore parts of this. Nothing can fix that from outside the app.
• Web page content is unaffected, by design. A browser's own interface is themed; the pages you visit are not.

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Built on a Sony VAIO SVE14A3AJ (2012) running Debian 13. Sharing is caring.