SDK Compatibility

Dark mode and Custom CSS need support on two sides: the Formbricks server that delivers the survey, and the SDK that shows it. This page lists the versions and explains what happens while they do not match yet. Upgrade in this order: the Formbricks server first, then your SDKs. A newer server never breaks an older SDK, and a newer SDK never breaks against an older server: surveys keep working, they only lack the new styling until both sides support it.

Minimum Versions

Component	Package	Dark mode (`setAppearance`)	Custom CSS
Formbricks server (self-hosted)	Formbricks	Pending release	Pending release
JavaScript, script tag	Served by your Formbricks server	Included with the server	Included with the server
JavaScript, npm	`@formbricks/js`	Pending release	Included with the server, no upgrade needed
iOS	`FormbricksSDK`	Pending release	Pending release
Android	`com.formbricks:android`	Pending release	Pending release
React Native	`@formbricks/react-native`	Pending release	Pending release
Flutter	`formbricks`	Pending release	Pending release

Formbricks Cloud always runs the current server. The JavaScript SDK loads its survey code from the server, so website and app surveys get Custom CSS as soon as the server supports it. Mobile SDKs have to pass Custom CSS to the survey themselves, so they need the release listed above.

Appearance

Every SDK shares one appearance contract:

Choose "light", "dark" or "system", either as the appearance setup option or with setAppearance at any time.
Without a choice, surveys render light.
setAppearance works before setup. The latest explicit choice wins: a later setup value or setAppearance call replaces an earlier one, and a setup without appearance keeps a choice made before it.
The choice is kept in memory for the current app or page session. It survives logout and identity reset, and is forgotten when the app restarts or the page reloads. It is not stored as a contact attribute and sends no request to Formbricks.
The appearance is applied before the survey first appears. Changing it while a survey is open switches the colors in place and keeps the respondent’s answers, progress and focus.

Setting the appearance with the JavaScript SDK

formbricks.setup({
  workspaceId: "<workspace-id>",
  appUrl: "<app-url>",
  appearance: "system", // "light" (default), "dark" or "system"
});

// When the user switches your app's theme:
formbricks.setAppearance("dark");

The mobile SDKs expose the same setAppearance method and setup option, using each platform’s usual enum or type. Their READMEs show the exact syntax.

What “system” Follows

"system" means the appearance your app is currently showing, which is not always the phone’s setting:

Platform	`"system"` follows
Website & app (JavaScript)	The browser’s `prefers-color-scheme`, updated live
iOS	The presenting view’s effective interface style, including an appearance your app or window overrides
Android	The host Activity’s `uiMode`, including an app-level night mode override
React Native	`Appearance.getColorScheme()`; an unknown value counts as light
Flutter	`Theme.of(context).brightness` where the survey is shown; the platform brightness when there is no theme

If your app keeps its theme only in its own code, such as a React context or an in-app toggle, "system" cannot see it. Call setAppearance("light") or setAppearance("dark") from that toggle instead.

Older Versions Without setAppearance

Check that the method exists before calling it, so older SDK versions keep working:

Feature-detecting setAppearance

if (typeof formbricks.setAppearance === "function") {
  formbricks.setAppearance("dark");
}

An SDK that has setAppearance but talks to an older self-hosted server accepts the call without an error. The survey stays light until the server is upgraded.

Custom CSS In Apps

Link surveys and website & app surveys get Custom CSS from the server. Nothing to change in your code.
Mobile apps need an SDK version with Custom CSS support. It passes both the workspace CSS and the survey CSS to the survey, in light and dark mode, whether or not the survey overrides the workspace theme.
Older mobile SDKs show surveys without any Custom CSS. They never apply only part of it, such as the survey CSS without the workspace CSS it builds on.

Saved changes reach respondents within about an hour, as SDKs refresh the survey configuration. A survey that is already open keeps the styling it opened with until the respondent finishes it.

Mixed Versions

Situation	What respondents see
New server, older mobile SDK	Surveys work as before: light, without Custom CSS
New server, older `@formbricks/js`	Custom CSS applies. `setAppearance` is not available yet, so surveys stay light
Older self-hosted server, new SDK	Surveys work and stay light, without Custom CSS. `setAppearance` is accepted and has no effect
No Custom CSS saved	The theme styling only, unchanged
Configuration cached before Custom CSS was saved	No Custom CSS until the SDK refreshes its configuration, at most about an hour later

Browser And WebView Support

Where	Supported	Renders, may look off
Link surveys, website & app surveys	Chrome and Edge 111+, Safari 16.4+, Firefox 128+	Chrome 99, Safari 15.4, Firefox 97 and later
iOS apps	iOS 16.4+ (WKWebView)	iOS 16.0 to 16.3
Android apps	Android System WebView 111+	WebView 99 to 110
React Native and Flutter apps	As iOS and Android above	As iOS and Android above

These are the browser versions the survey styles are built for. The SDKs keep their existing minimum OS versions. On a device below the supported range, surveys still open but colors and layout can be off.

Overview

Survey Features

Best Practices

Minimum Versions

Appearance

What “system” Follows

Older Versions Without setAppearance

Custom CSS In Apps

Mixed Versions

Browser And WebView Support

​Minimum Versions

​Appearance

​What “system” Follows

​Older Versions Without setAppearance

​Custom CSS In Apps

​Mixed Versions

​Browser And WebView Support

Minimum Versions

Appearance

What “system” Follows

Older Versions Without setAppearance

Custom CSS In Apps

Mixed Versions

Browser And WebView Support