Fix automatic readable text contrast for public and admin themes.

Derive admin/public text colors from WCAG contrast, unify ThemeVars CSS emission, and keep navbar overrides in sync with readable vars.

Co-authored-by: Cursor <[email protected]>

public/scripts/theme-init.js

@@ -1,4 +1,66 @@
 (() => {
+	function parseHex(value) {
+		const trimmed = String(value || "").trim();
+		const short = /^#([0-9a-f]{3})$/i.exec(trimmed);
+		if (short) {
+			const [r, g, b] = short[1].split("");
+			return [
+				Number.parseInt(r + r, 16),
+				Number.parseInt(g + g, 16),
+				Number.parseInt(b + b, 16),
+			];
+		}
+		const match = /^#([0-9a-f]{6})$/i.exec(trimmed);
+		if (!match) return null;
+		return [
+			Number.parseInt(match[1].slice(0, 2), 16),
+			Number.parseInt(match[1].slice(2, 4), 16),
+			Number.parseInt(match[1].slice(4, 6), 16),
+		];
+	}
+
+	function relativeLuminance(rgb) {
+		const channels = rgb.map((channel) => {
+			const value = channel / 255;
+			return value <= 0.04045
+				? value / 12.92
+				: ((value + 0.055) / 1.055) ** 2.4;
+		});
+		return 0.2126 * channels[0] + 0.7152 * channels[1] + 0.0722 * channels[2];
+	}
+
+	function contrastRatio(foreground, background) {
+		const fg = parseHex(foreground);
+		const bg = parseHex(background);
+		if (!fg || !bg) return null;
+		const light = Math.max(relativeLuminance(fg), relativeLuminance(bg));
+		const dark = Math.min(relativeLuminance(fg), relativeLuminance(bg));
+		return (light + 0.05) / (dark + 0.05);
+	}
+
+	function readableColor(preferred, background) {
+		const preferredRatio = contrastRatio(preferred, background);
+		if (preferredRatio != null && preferredRatio >= 4.5) return preferred;
+		const black = contrastRatio("#000000", background) ?? 0;
+		const white = contrastRatio("#ffffff", background) ?? 0;
+		return white >= black ? "#ffffff" : "#000000";
+	}
+
+	function applyNavbarColors(navbarColor, navbarTextColor) {
+		const root = document.documentElement.style;
+		if (navbarColor) root.setProperty("--color-navbar", navbarColor);
+		const text =
+			navbarTextColor ||
+			(navbarColor ? readableColor("#1e293b", navbarColor) : null);
+		if (text) {
+			root.setProperty("--color-navbar-text", text);
+			root.setProperty("--color-navbar-text-readable", text);
+		} else if (navbarColor) {
+			const readable = readableColor("#ffffff", navbarColor);
+			root.setProperty("--color-navbar-text-readable", readable);
+		}
+	}
+
 	let theme = null;
 	let defaultDark = false;
 	let navbarColor = null;
@@ -12,11 +74,5 @@
 	} catch (_e) {}
 	if (theme === "dark" || (!theme && defaultDark))
 		document.documentElement.classList.add("dark");
-	if (navbarColor)
-		document.documentElement.style.setProperty("--color-navbar", navbarColor);
-	if (navbarTextColor)
-		document.documentElement.style.setProperty(
-			"--color-navbar-text",
-			navbarTextColor,
-		);
+	applyNavbarColors(navbarColor, navbarTextColor);
 })();

src/app/admin/layout.tsx

@@ -402,7 +402,7 @@ async function Sidebar({
 		>
 			<div className="flex items-center gap-3 px-4 py-5 border-b border-[var(--admin-border)]">
 				<span
-					className="flex-none w-10 h-10 rounded-xl grid place-items-center font-extrabold text-base text-[var(--color-primary-foreground-readable)] bg-[var(--admin-accent)] shadow-lg shadow-[var(--admin-accent)]/20"
+					className="flex-none w-10 h-10 rounded-xl grid place-items-center font-extrabold text-base text-[var(--admin-accent-foreground)] bg-[var(--admin-accent)] shadow-lg shadow-[var(--admin-accent)]/20"
 					aria-hidden
 				>
 					{initial}
@@ -475,7 +475,7 @@ async function Topbar({
 				<span className="text-xs text-[var(--admin-text-muted)]">
 					<strong className="text-[var(--admin-text)]">{staff.username}</strong>
 				</span>
-				<span className="inline-flex items-center gap-1.5 text-[0.6rem] font-bold uppercase tracking-wider text-[var(--color-primary-foreground-readable)] bg-[var(--admin-accent)] rounded-full px-2.5 py-1">
+				<span className="inline-flex items-center gap-1.5 text-[0.6rem] font-bold uppercase tracking-wider text-[var(--admin-accent-foreground)] bg-[var(--admin-accent)] rounded-full px-2.5 py-1">
 					{t("rankLabel", { rank: staff.rank })}
 				</span>
 			</div>

src/app/admin/theme/color-field.tsx

@@ -73,7 +73,17 @@ export function ColorField({
 				type="color"
 				name={name}
 				value={val}
-				onChange={(e) => setVal(e.target.value)}
+				onChange={(e) => {
+					const next = e.target.value;
+					if (bgValue) {
+						const nextRatio = contrastRatio(next, bgValue);
+						if (nextRatio != null && nextRatio < 4.5) {
+							setVal(readableOn(bgValue));
+							return;
+						}
+					}
+					setVal(next);
+				}}
 				style={{
 					width: 42,
 					height: 36,

src/app/globals.css

@@ -86,12 +86,7 @@
 	--border-subtle: color-mix(in srgb, var(--color-text-muted) 18%, transparent);
 }
 
-/* Dark mode colors are generated by ThemeVars from the selected preset. */
-html.dark {
-	--color-text-readable: var(--color-text);
-	--color-text-muted-readable: var(--color-text-muted);
-	--color-navbar-text-readable: var(--color-navbar-text);
-}
+/* Dark mode colors + readable contrast vars are generated by ThemeVars. */
 html.dark input,
 html.dark select,
 html.dark textarea {

src/components/navbar-color-picker.tsx

@@ -39,6 +39,10 @@ export function NavbarColorPicker() {
 		if (!c) return;
 		document.documentElement.style.setProperty("--color-navbar", c.value);
 		document.documentElement.style.setProperty("--color-navbar-text", c.text);
+		document.documentElement.style.setProperty(
+			"--color-navbar-text-readable",
+			c.text,
+		);
 		try {
 			localStorage.setItem("navbarColor", c.value);
 			localStorage.setItem("navbarTextColor", c.text);
@@ -58,6 +62,10 @@ export function NavbarColorPicker() {
 				"--color-navbar-text",
 				savedText,
 			);
+			document.documentElement.style.setProperty(
+				"--color-navbar-text-readable",
+				savedText,
+			);
 		}
 		setMounted(true);
 	}, []);

src/lib/theme-contrast.test.ts

@@ -130,6 +130,48 @@ describe("deriveAdminPalette", () => {
 		expect(admin.canvas).not.toBe("#ff00ff");
 		expect(admin.surface).not.toBe("#00ff00");
 	});
+
+	it("repairs default light text when admin canvas is forced light", () => {
+		const admin = deriveAdminPalette(
+			{ color_primary: "#f59e0b" },
+			{
+				canvas: "#ffffff",
+				surface: "#f8fafc",
+				surfaceElevated: "#f1f5f9",
+				sidebar: "#ffffff",
+			},
+		);
+		expect(contrastRatio(admin.text, admin.canvas)).toBeGreaterThanOrEqual(4.5);
+		expect(contrastRatio(admin.text, admin.surface)).toBeGreaterThanOrEqual(4.5);
+		expect(contrastRatio(admin.muted, admin.surface)).toBeGreaterThanOrEqual(
+			4.5,
+		);
+		expect(
+			contrastRatio(admin.sidebarText, admin.sidebar),
+		).toBeGreaterThanOrEqual(4.5);
+		expect(
+			contrastRatio(admin.accentForeground, admin.accent),
+		).toBeGreaterThanOrEqual(4.5);
+	});
+
+	it("repairs hostile admin text overrides on dark canvas", () => {
+		const admin = deriveAdminPalette(
+			{ color_primary: "#111827" },
+			{
+				canvas: "#0b0f19",
+				surface: "#151b27",
+				text: "#0b0f19",
+				muted: "#111827",
+			},
+		);
+		expect(contrastRatio(admin.text, admin.canvas)).toBeGreaterThanOrEqual(4.5);
+		expect(contrastRatio(admin.muted, admin.surface)).toBeGreaterThanOrEqual(
+			4.5,
+		);
+		expect(
+			contrastRatio(admin.accentForeground, admin.accent),
+		).toBeGreaterThanOrEqual(4.5);
+	});
 });
 
 describe("derivePublicForegrounds", () => {

src/lib/theme-contrast.ts

@@ -31,7 +31,7 @@ export function deriveAdminPalette(
 	colors: PublicThemeColors,
 	overrides?: Partial<AdminPalette>,
 ): AdminPalette {
-	const accent = colors.color_primary ?? "#f59e0b";
+	const accent = overrides?.accent ?? colors.color_primary ?? "#f59e0b";
 	const defaults: AdminPalette = {
 		canvas: "#0b0f19",
 		surface: "#151b27",
@@ -40,8 +40,8 @@ export function deriveAdminPalette(
 		muted: "#94a3b8",
 		border: "#2a3448",
 		accent,
-		accentText: readableColor(accent, ["#0b0f19", "#151b27", "#1e2635"]),
-		accentForeground: readableColor("#ffffff", [accent]),
+		accentText: "#f59e0b",
+		accentForeground: "#ffffff",
 		success: "#22c55e",
 		warning: "#eab308",
 		error: "#ef4444",
@@ -51,29 +51,35 @@ export function deriveAdminPalette(
 		overlay: "rgba(2, 6, 23, 0.72)",
 		focusRing: accent,
 	};
-	if (!overrides) return defaults;
-	return {
+
+	const merged: AdminPalette = {
 		...defaults,
 		...overrides,
 		accent,
-		accentText: readableColor(accent, [
-			overrides.canvas ?? defaults.canvas,
-			overrides.surface ?? defaults.surface,
-			overrides.surfaceElevated ?? defaults.surfaceElevated,
-		]),
-		accentForeground: readableColor("#ffffff", [accent]),
-		success: overrides.success ?? defaults.success,
-		warning: overrides.warning ?? defaults.warning,
-		error: overrides.error ?? defaults.error,
-		info: overrides.info ?? defaults.info,
-		sidebarText: readableColor(overrides.text ?? defaults.text, [
-			overrides.sidebar ?? defaults.sidebar,
-			overrides.canvas ?? defaults.canvas,
-			overrides.surface ?? defaults.surface,
-		]),
-		overlay: defaults.overlay,
+		overlay: overrides?.overlay ?? defaults.overlay,
 		focusRing: accent,
 	};
+
+	const surfaces = [
+		merged.canvas,
+		merged.surface,
+		merged.surfaceElevated,
+	] as const;
+	const preferredText = merged.text;
+	const preferredMuted = merged.muted;
+
+	return {
+		...merged,
+		text: readableColor(preferredText, surfaces),
+		muted: readableColor(preferredMuted, [merged.canvas, merged.surface]),
+		accentText: readableColor(accent, surfaces),
+		accentForeground: readableColor("#ffffff", [accent]),
+		sidebarText: readableColor(preferredText, [
+			merged.sidebar,
+			merged.canvas,
+			merged.surface,
+		]),
+	};
 }
 
 export function derivePublicForegrounds(c: PublicThemeColors) {
@@ -181,7 +187,17 @@ export function readableColor(
 }
 
 function parseHex(value: string): Rgb | null {
-	const match = /^#([0-9a-f]{6})$/i.exec(value.trim());
+	const trimmed = value.trim();
+	const short = /^#([0-9a-f]{3})$/i.exec(trimmed);
+	if (short) {
+		const [r, g, b] = short[1].split("");
+		return [
+			Number.parseInt(r + r, 16),
+			Number.parseInt(g + g, 16),
+			Number.parseInt(b + b, 16),
+		];
+	}
+	const match = /^#([0-9a-f]{6})$/i.exec(trimmed);
 	if (!match) return null;
 	return [
 		Number.parseInt(match[1].slice(0, 2), 16),

src/lib/theme-css.ts

@@ -40,12 +40,14 @@ export function adminPaletteCss(admin: AdminPalette): string {
 		`--admin-sidebar-background:${admin.sidebar};`,
 		`--admin-sidebar-text-readable:${admin.sidebarText};`,
 		`--admin-sidebar-muted-readable:color-mix(in srgb, var(--admin-sidebar-text-readable) 60%, transparent);`,
-		`--admin-input-text-readable:${readableColor(admin.text, [admin.canvas, admin.surface])};`,
+		`--admin-input-text-readable:${admin.text};`,
 		`--admin-canvas:${admin.canvas};`,
 		`--admin-surface:${admin.surface};`,
 		`--admin-surface-elevated:${admin.surfaceElevated};`,
 		`--admin-text:${admin.text};`,
+		`--admin-text-readable:${admin.text};`,
 		`--admin-text-muted:${admin.muted};`,
+		`--admin-text-muted-readable:${admin.muted};`,
 		`--admin-border:${admin.border};`,
 		`--admin-accent:${admin.accent};`,
 		`--admin-accent-text:${admin.accentText};`,
@@ -104,9 +106,7 @@ export function themePaletteCss(
 			`--color-${status}-subtle:color-mix(in srgb, ${palette[`color_${status}`]} 14%, ${palette.color_surface});`,
 			`--color-${status}-border:color-mix(in srgb, ${palette[`color_${status}`]} 38%, transparent);`,
 		]),
+		adminPaletteCss(admin),
 	);
-	if (adminOverrides || selector !== ":root") {
-		declarations.push(adminPaletteCss(admin));
-	}
 	return `${selector}{${declarations.join("")}}`;
 }