feat(gerrit): add some basic theming

This is based on some of the preliminary colour work done by @ckie in
the the-distro/floral.systems repo.

services/gerrit/default.nix

@@ -141,7 +141,9 @@ in
       plugins = with pkgs.gerritPlugins; [
         oauth
         metrics-reporter-prometheus
-        # Buildbot checks plugin (writeText because services.gerrit.plugins expects packages)
+        # Theme plugin
+        (pkgs.concatText "theme.js" [ ./theme.js ])
+        # Buildbot checks plugin
         (pkgs.runCommand "checks.js" {
           BASE_URI = builtins.toJSON "https://buildbot.forkos.org";
           SUPPORTED_PROJECTS = builtins.toJSON [

services/gerrit/theme.js

@@ -0,0 +1,69 @@
+/* Set up theming for Floral.
+ * vim: set et ts=2 sw=2:
+ */
+Gerrit.install((plugin) => {
+  const stylesheet = new CSSStyleSheet();
+  stylesheet.replace(`
+    html {
+      --header-title-content: 'floral.systems';
+
+      --blue-50: #f3f4fb;
+      --blue-100: #e3e6f6;
+      --blue-200: #ced5ef;
+      --blue-300: #acb8e4;
+      --blue-400: #8495d6;
+      --blue-500: #6775ca;
+      --blue-600: #5158bb;
+      --blue-700: #494bac;
+      --blue-800: #41408d;
+      --blue-900: #383870;
+      --blue-950: #252546;
+
+      --coral-50: #fff1f1;
+      --coral-100: #ffe0e0;
+      --coral-200: #ffc5c5;
+      --coral-300: #ff9e9d;
+      --coral-400: #ff6665;
+      --coral-500: #fe4a49;
+      --coral-600: #ec1716;
+      --coral-700: #c70f0e;
+      --coral-800: #a41110;
+      --coral-900: #881514;
+      --coral-950: #4a0505;
+
+      --teal-50: #eefbf5;
+      --teal-100: #d6f5e5;
+      --teal-200: #b1e9d0;
+      --teal-300: #7ed7b5;
+      --teal-400: #49be95;
+      --teal-500: #27a27b;
+      --teal-600: #188162;
+      --teal-700: #136951;
+      --teal-800: #125342;
+      --teal-900: #104437;
+      --teal-950: #08261f;
+
+      --zinc-50: #fafafa;
+      --zinc-100: #f4f4f5;
+      --zinc-200: #e4e4e7;
+      --zinc-300: #d4d4d8;
+      --zinc-400: #a1a1aa;
+      --zinc-500: #71717a;
+      --zinc-600: #52525b;
+      --zinc-700: #3f3f46;
+      --zinc-800: #27272a;
+      --zinc-900: #18181b;
+      --zinc-950: #09090b;
+    }
+    html.lightTheme {
+      --header-background-color: var(--teal-700);
+      --header-text-color: var(--coral-50);
+    }
+    html.darkTheme {
+      --header-background-color: var(--teal-900);
+      --header-text-color: var(--coral-50);
+    }
+  `).then(() => {
+    document.adoptedStyleSheets = [...document.adoptedStyleSheets, stylesheet];
+  });
+});