diff --git a/src/lib/utils/theme-persist.ts b/src/lib/utils/theme-persist.ts
new file mode 100644
index 0000000..4ab1f7a
--- /dev/null
+++ b/src/lib/utils/theme-persist.ts
@@ -0,0 +1,93 @@
+import type { TenantThemeData } from '../../app.d.js';
+
+/**
+ * Client-side CSS variable mapping — mirrors server-side theme-css.ts
+ */
+const FIELD_MAP: Record<string, { cssVar: string; mode: 'light' | 'dark' }> = {};
+
+const vars = [
+	['PageBg', '--color-page-bg'],
+	['NavBg', '--color-nav-bg'],
+	['ColumnBg', '--color-column-bg'],
+	['ColumnBorder', '--color-column-border'],
+	['ColumnText', '--color-column-text'],
+	['CardBg', '--color-card-bg'],
+	['CardBorder', '--color-card-border'],
+	['CardText', '--color-card-text'],
+	['CardRadius', '--color-card-radius'],
+	['Primary', '--color-primary'],
+	['PrimaryHover', '--color-primary-hover'],
+	['Danger', '--color-danger'],
+	['DangerHover', '--color-danger-hover'],
+	['Success', '--color-success'],
+	['Warning', '--color-warning']
+] as const;
+
+for (const [suffix, cssVar] of vars) {
+	FIELD_MAP[`light${suffix}`] = { cssVar, mode: 'light' };
+	FIELD_MAP[`dark${suffix}`] = { cssVar, mode: 'dark' };
+}
+
+function hexToRgba(hex: string, opacity: number): string {
+	const h = hex.replace('#', '');
+	const r = parseInt(h.substring(0, 2), 16);
+	const g = parseInt(h.substring(2, 4), 16);
+	const b = parseInt(h.substring(4, 6), 16);
+	return `rgba(${r}, ${g}, ${b}, ${opacity})`;
+}
+
+/**
+ * Generates CSS from theme data and writes it into the <style id="tenant-theme"> element.
+ * This mirrors what generateTenantCSS does server-side, but runs in the browser
+ * so theme changes take effect immediately without a full page reload.
+ */
+export function persistThemeCSS(theme: TenantThemeData) {
+	const lightVars: string[] = [];
+	const darkVars: string[] = [];
+
+	for (const [field, { cssVar, mode }] of Object.entries(FIELD_MAP)) {
+		const value = (theme as any)[field];
+		if (value == null) continue;
+		const target = mode === 'dark' ? darkVars : lightVars;
+		target.push(`  ${cssVar}: ${value};`);
+	}
+
+	// Handle opacity for columns
+	if (theme.lightColumnOpacity != null && theme.lightColumnBg?.startsWith('#')) {
+		const idx = lightVars.findIndex((v) => v.includes('--color-column-bg:'));
+		if (idx !== -1) lightVars[idx] = `  --color-column-bg: ${hexToRgba(theme.lightColumnBg, theme.lightColumnOpacity)};`;
+		if (theme.lightColumnOpacity < 1) lightVars.push(`  --column-backdrop-blur: blur(8px);`);
+	}
+	if (theme.lightCardOpacity != null && theme.lightCardBg?.startsWith('#')) {
+		const idx = lightVars.findIndex((v) => v.includes('--color-card-bg:'));
+		if (idx !== -1) lightVars[idx] = `  --color-card-bg: ${hexToRgba(theme.lightCardBg, theme.lightCardOpacity)};`;
+		if (theme.lightCardOpacity < 1) lightVars.push(`  --card-backdrop-blur: blur(8px);`);
+	}
+	if (theme.darkColumnOpacity != null && theme.darkColumnBg?.startsWith('#')) {
+		const idx = darkVars.findIndex((v) => v.includes('--color-column-bg:'));
+		if (idx !== -1) darkVars[idx] = `  --color-column-bg: ${hexToRgba(theme.darkColumnBg, theme.darkColumnOpacity)};`;
+		if (theme.darkColumnOpacity < 1) darkVars.push(`  --column-backdrop-blur: blur(8px);`);
+	}
+	if (theme.darkCardOpacity != null && theme.darkCardBg?.startsWith('#')) {
+		const idx = darkVars.findIndex((v) => v.includes('--color-card-bg:'));
+		if (idx !== -1) darkVars[idx] = `  --color-card-bg: ${hexToRgba(theme.darkCardBg, theme.darkCardOpacity)};`;
+		if (theme.darkCardOpacity < 1) darkVars.push(`  --card-backdrop-blur: blur(8px);`);
+	}
+
+	let css = '';
+	if (lightVars.length > 0) {
+		css += `:root {\n${lightVars.join('\n')}\n}\n`;
+	}
+	if (darkVars.length > 0) {
+		css += `html.dark {\n${darkVars.join('\n')}\n}\n`;
+	}
+
+	// Find or create the <style id="tenant-theme"> element
+	let styleEl = document.getElementById('tenant-theme') as HTMLStyleElement | null;
+	if (!styleEl) {
+		styleEl = document.createElement('style');
+		styleEl.id = 'tenant-theme';
+		document.head.appendChild(styleEl);
+	}
+	styleEl.textContent = css;
+}
diff --git a/src/routes/admin/branding/+page.server.ts b/src/routes/admin/branding/+page.server.ts
index d2c3009..6b80008 100644
--- a/src/routes/admin/branding/+page.server.ts
+++ b/src/routes/admin/branding/+page.server.ts
@@ -8,19 +8,14 @@ export const load: PageServerLoad = async ({ locals }) => {
 	if (!tenant) throw error(400, 'Unknown tenant');
 	requireTenantAdmin(locals.user);
 
-	const [theme, tenantData] = await withTenant(tenant.id, async (tx) => {
-		const t = await tx.tenantTheme.findUnique({ where: { tenantId: tenant.id } });
-		const td = await tx.tenant.findUnique({
-			where: { id: tenant.id },
-			select: { logoUrl: true, logoText: true }
-		});
-		return [t, td] as const;
+	const theme = await withTenant(tenant.id, async (tx) => {
+		return tx.tenantTheme.findUnique({ where: { tenantId: tenant.id } });
 	});
 
 	return {
 		theme: theme ?? null,
 		tenantName: tenant.name,
-		logoUrl: tenantData?.logoUrl ?? null,
-		logoText: tenantData?.logoText ?? null
+		logoUrl: tenant.logoUrl ?? null,
+		logoText: tenant.logoText ?? null
 	};
 };
diff --git a/src/routes/admin/branding/+page.svelte b/src/routes/admin/branding/+page.svelte
index 2b83052..c98cb51 100644
--- a/src/routes/admin/branding/+page.svelte
+++ b/src/routes/admin/branding/+page.svelte
@@ -5,6 +5,7 @@
 	import { toast } from '$lib/stores/toasts.svelte.js';
 	import { getTheme } from '$lib/stores/theme.svelte.js';
 	import { applyThemePreview, clearThemePreview } from '$lib/utils/theme-preview.js';
+	import { persistThemeCSS } from '$lib/utils/theme-persist.js';
 	import ColorPicker from '$lib/components/ColorPicker.svelte';
 	import ImageUploadField from '$lib/components/ImageUploadField.svelte';
 	import type { TenantThemeData } from '../../../app.d.js';
@@ -55,6 +56,7 @@
 			body: JSON.stringify({ ...draft, logoText: logoText || null })
 		});
 		if (ok) {
+			persistThemeCSS(draft);
 			toast.success('Theme saved');
 			await invalidateAll();
 		}
@@ -84,6 +86,7 @@
 		if (ok) {
 			draft = {};
 			clearThemePreview();
+			persistThemeCSS({});
 			toast.success('Theme reset to defaults');
 			await invalidateAll();
 		}