diff --git a/.gitignore b/.gitignore
index 860119d..ea3e2dc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,3 +16,7 @@ __pycache__/
 
 # Generated from the colour scheme; machine state, not configuration.
 /config/dot/kitty/current-theme.conf
+
+# Generated from the colour scheme; machine state, not configuration.
+/config/dot/gtk-3.0/settings.ini
+/config/dot/gtk-4.0/settings.ini
diff --git a/config/dot/gtk-3.0/settings.ini b/config/dot/gtk-3.0/settings.ini.template
similarity index 60%
rename from config/dot/gtk-3.0/settings.ini
rename to config/dot/gtk-3.0/settings.ini.template
index 02eb639..e4ebce2 100644
--- a/config/dot/gtk-3.0/settings.ini
+++ b/config/dot/gtk-3.0/settings.ini.template
@@ -1,3 +1,12 @@
+# GENERATED FILE -- edit settings.ini.template instead.
+#
+# The theme name and dark preference below follow Panama's colour
+# scheme, so this file is regenerated on every switch and is not
+# committed. Under GNOME, gnome-settings-daemon publishes these over
+# XSETTINGS and this file is ignored; under Hyprland there is no
+# settings daemon, so for GTK3 it is authoritative -- which is why it
+# has to change with the scheme rather than being pinned to dark.
+#
 [Settings]
 # These values must match `gsettings get org.gnome.desktop.interface ...`.
 #
@@ -6,12 +15,12 @@
 # this file becomes authoritative for GTK3 — which is why it previously named
 # themes that aren't installed (Tahoe-Dark, WhiteSur-cursors) without anything
 # appearing broken.
-gtk-theme-name=adw-gtk3-dark
+gtk-theme-name=@GTK_THEME@
 gtk-icon-theme-name=Adwaita
 gtk-font-name=Adwaita Sans 11
 gtk-cursor-theme-name=oreo_blue_cursors
 gtk-cursor-theme-size=24
-gtk-application-prefer-dark-theme=1
+gtk-application-prefer-dark-theme=@PREFER_DARK@
 
 gtk-toolbar-style=GTK_TOOLBAR_ICONS
 gtk-toolbar-icon-size=GTK_ICON_SIZE_LARGE_TOOLBAR
diff --git a/config/dot/gtk-4.0/settings.ini b/config/dot/gtk-4.0/settings.ini
deleted file mode 100644
index bb748bb..0000000
--- a/config/dot/gtk-4.0/settings.ini
+++ /dev/null
@@ -1,11 +0,0 @@
-[Settings]
-# libadwaita apps normally take their dark preference from the
-# org.freedesktop.appearance portal (served by xdg-desktop-portal-gtk, which
-# reads gsettings). This file is the fallback for plain GTK4 apps and for the
-# window before the portal answers.
-gtk-application-prefer-dark-theme=1
-gtk-theme-name=adw-gtk3-dark
-gtk-icon-theme-name=Adwaita
-gtk-font-name=Adwaita Sans 11
-gtk-cursor-theme-name=oreo_blue_cursors
-gtk-cursor-theme-size=24
diff --git a/config/dot/gtk-4.0/settings.ini.template b/config/dot/gtk-4.0/settings.ini.template
new file mode 100644
index 0000000..973a818
--- /dev/null
+++ b/config/dot/gtk-4.0/settings.ini.template
@@ -0,0 +1,20 @@
+# GENERATED FILE -- edit settings.ini.template instead.
+#
+# The theme name and dark preference below follow Panama's colour
+# scheme, so this file is regenerated on every switch and is not
+# committed. Under GNOME, gnome-settings-daemon publishes these over
+# XSETTINGS and this file is ignored; under Hyprland there is no
+# settings daemon, so for GTK3 it is authoritative -- which is why it
+# has to change with the scheme rather than being pinned to dark.
+#
+[Settings]
+# libadwaita apps normally take their dark preference from the
+# org.freedesktop.appearance portal (served by xdg-desktop-portal-gtk, which
+# reads gsettings). This file is the fallback for plain GTK4 apps and for the
+# window before the portal answers.
+gtk-application-prefer-dark-theme=@PREFER_DARK@
+gtk-theme-name=@GTK_THEME@
+gtk-icon-theme-name=Adwaita
+gtk-font-name=Adwaita Sans 11
+gtk-cursor-theme-name=oreo_blue_cursors
+gtk-cursor-theme-size=24
diff --git a/config/dot/quickshell/scripts/panama-theme-apps b/config/dot/quickshell/scripts/panama-theme-apps
index 8b2708e..a33ff31 100755
--- a/config/dot/quickshell/scripts/panama-theme-apps
+++ b/config/dot/quickshell/scripts/panama-theme-apps
@@ -11,6 +11,11 @@
 # Terminals are the notable exception -- they predate the standard and carry
 # their own palettes. kitty is handled here.
 #
+# GTK3 is the other one. Under GNOME, gnome-settings-daemon publishes the theme
+# over XSETTINGS; under Hyprland nothing does, so ~/.config/gtk-3.0/settings.ini
+# is authoritative for GTK3 applications. Pinned to dark, it contradicted the
+# scheme in light mode, so it is generated from a template here instead.
+#
 #   panama-theme-apps dark|light
 #
 # kitty gets it twice: the generated include file so terminals opened later
@@ -26,6 +31,36 @@ case "$scheme" in
     *) printf 'usage: panama-theme-apps [dark|light]\n' >&2; exit 2 ;;
 esac
 
+# ── GTK ──────────────────────────────────────────────────────────────────────
+# adw-gtk3, not Adwaita: no Adwaita GTK theme is installed on Fedora 44, and
+# naming a theme that does not exist makes GTK fall back to its light default --
+# which made dark mode silently produce light windows.
+if [[ "$scheme" == "light" ]]; then
+    gtk_theme="adw-gtk3"
+    prefer_dark=0
+else
+    gtk_theme="adw-gtk3-dark"
+    prefer_dark=1
+fi
+
+status_gtk="skipped"
+for gtk_version in 3.0 4.0; do
+    gtk_dir="${XDG_CONFIG_HOME:-$HOME/.config}/gtk-$gtk_version"
+    template="$gtk_dir/settings.ini.template"
+    [[ -r "$template" ]] || continue
+
+    # Written atomically: a GTK application starting mid-write would otherwise
+    # read a truncated file and fall back to defaults.
+    if sed -e "s/@GTK_THEME@/$gtk_theme/" -e "s/@PREFER_DARK@/$prefer_dark/" "$template" \
+        >"$gtk_dir/settings.ini.tmp" 2>/dev/null \
+        && mv "$gtk_dir/settings.ini.tmp" "$gtk_dir/settings.ini" 2>/dev/null; then
+        status_gtk="written"
+    else
+        rm -f "$gtk_dir/settings.ini.tmp"
+        status_gtk="failed"
+    fi
+done
+
 kitty_dir="${XDG_CONFIG_HOME:-$HOME/.config}/kitty"
 theme_file="$kitty_dir/themes/tokyonight-moon.conf"
 [[ "$scheme" == "light" ]] && theme_file="$kitty_dir/themes/tokyonight-day.conf"
diff --git a/config/dot/quickshell/services/ColorScheme.qml b/config/dot/quickshell/services/ColorScheme.qml
index 4f09838..2de1c7b 100644
--- a/config/dot/quickshell/services/ColorScheme.qml
+++ b/config/dot/quickshell/services/ColorScheme.qml
@@ -78,9 +78,21 @@ Singleton {
         root.lastError = "";
 
         const scheme = root.dark ? "prefer-dark" : "prefer-light";
-        // Adwaita's light and dark are the same theme; only the preference and
-        // the -dark suffix differ, so applications that honour either agree.
-        const gtkTheme = root.dark ? "Adwaita-dark" : "Adwaita";
+
+        // adw-gtk3, not Adwaita. This is the bug that made dark mode look
+        // broken while light mode looked fine:
+        //
+        // Neither "Adwaita" nor "Adwaita-dark" is an installed theme on Fedora
+        // 44 -- only adw-gtk3 and adw-gtk3-dark are. Naming a theme that does
+        // not exist makes GTK fall back to its built-in default, which is
+        // LIGHT. So asking for light accidentally worked, asking for dark
+        // silently produced light, and applications that take their cue from
+        // the GTK theme rather than the portal -- Chromium and Electron, when
+        // built against GTK -- stayed light no matter what the portal said.
+        //
+        // gtk-theme-contract asserts these names are actually installed,
+        // because the failure mode is silent in exactly this way.
+        const gtkTheme = root.dark ? "adw-gtk3-dark" : "adw-gtk3";
 
         const commands = [
             ["gsettings", "set", "org.gnome.desktop.interface", "color-scheme", scheme],
diff --git a/setup/scripts/link-dotfiles b/setup/scripts/link-dotfiles
index b3e0fde..352480b 100755
--- a/setup/scripts/link-dotfiles
+++ b/setup/scripts/link-dotfiles
@@ -70,6 +70,34 @@ for dir in "${dirs[@]}"; do
   log "Linked $PANAMA_DOT/$dir → $CONFIG/$dir"
 done
 
+# GTK3 has no include mechanism, so its settings.ini is generated whole from a
+# template rather than layered. Without this, a fresh checkout has a template
+# and no settings.ini, and GTK3 applications fall back to their built-in theme.
+# panama-theme-apps rewrites both files on every scheme change after this.
+for gtk_version in 3.0 4.0; do
+  gtk_template="$PANAMA_DOT/gtk-$gtk_version/settings.ini.template"
+  gtk_settings="$PANAMA_DOT/gtk-$gtk_version/settings.ini"
+  [ -r "$gtk_template" ] || continue
+  if [ -e "$gtk_settings" ]; then
+    log "Keeping existing GTK settings at $gtk_settings"
+  else
+    gtk_scheme="dark"
+    gtk_prefs="${XDG_CONFIG_HOME:-$HOME/.config}/panama/settings.json"
+    if [ -r "$gtk_prefs" ]; then
+      gtk_stored="$(jq -r '.colorScheme // "dark"' "$gtk_prefs" 2>/dev/null || echo dark)"
+      [ "$gtk_stored" = "light" ] && gtk_scheme="light"
+    fi
+    if [ "$gtk_scheme" = "light" ]; then
+      gtk_name="adw-gtk3"; gtk_dark=0
+    else
+      gtk_name="adw-gtk3-dark"; gtk_dark=1
+    fi
+    sed -e "s/@GTK_THEME@/$gtk_name/" -e "s/@PREFER_DARK@/$gtk_dark/" \
+      "$gtk_template" > "$gtk_settings"
+    log "Generated GTK $gtk_version settings ($gtk_name) → $gtk_settings"
+  fi
+done
+
 # kitty.conf ends with `include current-theme.conf`, and that file is generated
 # from the desktop colour scheme rather than committed -- it is machine state.
 # A fresh checkout therefore has no such file, and kitty starts by complaining
diff --git a/tests/quickshell/gtk-theme-contract.sh b/tests/quickshell/gtk-theme-contract.sh
new file mode 100755
index 0000000..07e0b26
--- /dev/null
+++ b/tests/quickshell/gtk-theme-contract.sh
@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+
+# Every GTK theme name Panama sets must be a theme that is actually installed.
+#
+# This exists because of a bug that was invisible for weeks. ColorScheme set
+# gtk-theme to "Adwaita-dark" for dark and "Adwaita" for light. Neither is
+# installed on Fedora 44 -- only adw-gtk3 and adw-gtk3-dark are -- and GTK
+# responds to an unknown theme name by silently falling back to its built-in
+# default, which is LIGHT.
+#
+# So light mode appeared to work, dark mode produced light windows, and nothing
+# anywhere reported an error. Applications that take their cue from the GTK
+# theme rather than the portal -- Chromium and Electron among them -- were stuck
+# light with no way to diagnose it from inside the application.
+#
+# The failure is silent by construction, so it needs a test rather than a
+# comment. Checks the compositor-facing setting and the generated GTK config
+# agree, and that both name something real.
+
+set -uo pipefail
+
+repo_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+color_scheme="$repo_dir/config/dot/quickshell/services/ColorScheme.qml"
+theme_apps="$repo_dir/config/dot/quickshell/scripts/panama-theme-apps"
+
+fail() {
+    printf 'gtk theme contract: %s\n' "$1" >&2
+    exit 1
+}
+
+theme_installed() {
+    local name="$1" dir
+    for dir in /usr/share/themes "$HOME/.themes" "$HOME/.local/share/themes"; do
+        [[ -d "$dir/$name/gtk-3.0" ]] && return 0
+    done
+    return 1
+}
+
+# ── The names ColorScheme sets must exist ────────────────────────────────────
+names="$(grep -oE 'root\.dark \? "[a-zA-Z0-9-]+" : "[a-zA-Z0-9-]+"' "$color_scheme" \
+    | grep -oE '"[a-zA-Z0-9-]+"' | tr -d '"' | grep -E '^adw-|^Adwaita' | sort -u)"
+[[ -n "$names" ]] || fail 'could not find the GTK theme names in ColorScheme.qml -- this contract is not reading it correctly'
+
+while read -r name; do
+    [[ -n "$name" ]] || continue
+    theme_installed "$name" \
+        || fail "ColorScheme sets gtk-theme to \"$name\", which is not installed. GTK falls back to its light default when a theme is missing, so this produces light windows in dark mode with no error anywhere."
+done <<<"$names"
+
+# ── The generated GTK config must agree, in both directions ──────────────────
+# Generated into a fixture rather than the live config, so running this cannot
+# retheme the desktop it is running on.
+fixture="$(mktemp -d /tmp/panama-gtk-theme.XXXXXX)"
+trap 'rm -rf "$fixture"' EXIT
+
+for version in 3.0 4.0; do
+    mkdir -p "$fixture/gtk-$version"
+    cp "$repo_dir/config/dot/gtk-$version/settings.ini.template" "$fixture/gtk-$version/" \
+        || fail "gtk-$version has no settings.ini.template -- the generated file would never be produced"
+done
+
+for scheme in dark light; do
+    XDG_CONFIG_HOME="$fixture" "$theme_apps" "$scheme" >/dev/null 2>&1
+
+    for version in 3.0 4.0; do
+        generated="$fixture/gtk-$version/settings.ini"
+        [[ -r "$generated" ]] || fail "gtk-$version settings.ini was not generated for $scheme"
+
+        grep -q '@GTK_THEME@\|@PREFER_DARK@' "$generated" \
+            && fail "gtk-$version settings.ini still contains an unsubstituted placeholder for $scheme"
+
+        theme="$(sed -n 's/^gtk-theme-name=//p' "$generated")"
+        prefer="$(sed -n 's/^gtk-application-prefer-dark-theme=//p' "$generated")"
+
+        theme_installed "$theme" \
+            || fail "gtk-$version settings.ini names \"$theme\" for $scheme, which is not installed"
+
+        if [[ "$scheme" == "dark" ]]; then
+            [[ "$prefer" == "1" ]] || fail "gtk-$version asks for prefer-dark=$prefer in dark mode"
+            [[ "$theme" == *dark* ]] || fail "gtk-$version uses \"$theme\" in dark mode, which is not a dark theme"
+        else
+            [[ "$prefer" == "0" ]] || fail "gtk-$version asks for prefer-dark=$prefer in light mode"
+            [[ "$theme" != *dark* ]] || fail "gtk-$version uses \"$theme\" in light mode, which is a dark theme"
+        fi
+    done
+done
+
+printf 'gtk theme contract: PASS\n'