Custom UI

Prerequisite: Ensure ClerkProvider wraps your app. See setup/.

Version: Check package.json for the SDK version — see clerk skill for the version table. This determines which custom flow references to use below.

This skill covers two areas:

1. Custom authentication flows — build your own sign-in/sign-up UI with hooks
2. Appearance customization — theme, style, and brand Clerk's pre-built components

Custom Flow References

Task	Core 2	Current
Custom sign-in (useSignIn)	core-2/custom-sign-in.md	core-3/custom-sign-in.md
Custom sign-up (useSignUp)	core-2/custom-sign-up.md	core-3/custom-sign-up.md
<Show> component	(use <SignedIn>, <SignedOut>, <Protect>)	core-3/show-component.md

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Appearance Customization

Appearance customization applies to both Core 2 and the current SDK.

Component Customization Options

Task	Documentation
Appearance prop overview	https://clerk.com/docs/nextjs/guides/customizing-clerk/appearance-prop/overview
Options (structure, logo, buttons)	https://clerk.com/docs/nextjs/guides/customizing-clerk/appearance-prop/layout
Themes (pre-built dark/light)	https://clerk.com/docs/nextjs/guides/customizing-clerk/appearance-prop/themes
Variables (colors, fonts, spacing)	https://clerk.com/docs/nextjs/guides/customizing-clerk/appearance-prop/variables
CAPTCHA configuration	https://clerk.com/docs/nextjs/guides/customizing-clerk/appearance-prop/captcha
Bring your own CSS	https://clerk.com/docs/nextjs/guides/customizing-clerk/appearance-prop/bring-your-own-css

Appearance Pattern

<SignIn
  appearance={{
    variables: {
      colorPrimary: '#0000ff',
      borderRadius: '0.5rem',
    },
    options: {
      logoImageUrl: '/logo.png',
      socialButtonsVariant: 'iconButton',
    },
  }}
/>

Core 2 ONLY (skip if current SDK): The options property was named layout. Use layout: { logoImageUrl: '...', socialButtonsVariant: '...' } instead of options.

variables (colors, typography, borders)

Property	Description
colorPrimary	Primary color throughout
colorBackground	Background color
borderRadius	Border radius (default: 0.375rem)

Opacity change: colorRing and colorModalBackdrop now render at full opacity. Use explicit rgba() values if you need transparency.

Core 2 ONLY (skip if current SDK): colorRing and colorModalBackdrop rendered at 15% opacity by default.

options (structure, logo, social buttons)

Property	Description
logoImageUrl	URL to custom logo
socialButtonsVariant	'blockButton' | 'iconButton' | 'auto'
socialButtonsPlacement	'top' | 'bottom'
showOptionalFields	Show optional fields (default: false)

Core 2 ONLY (skip if current SDK): This property is called layout, not options. Also, showOptionalFields defaulted to true.

Themes

Install themes from @clerk/ui:

npm install @clerk/ui

import { dark } from '@clerk/ui/themes'

<ClerkProvider appearance={{ theme: dark }} />

Core 2 ONLY (skip if current SDK): Themes are imported from @clerk/themes (install @clerk/themes instead of @clerk/ui). Example: import { dark } from '@clerk/themes'.

Theme stacking — pass an array where the last theme takes precedence:

import { dark, neobrutalism } from '@clerk/ui/themes'

<ClerkProvider appearance={{ theme: [dark, neobrutalism] }} />

CSS color-scheme support — the default theme respects the CSS color-scheme property for automatic light/dark mode toggling.

Available themes: dark, neobrutalism, shadcn, simple

shadcn Theme (HIGH PRIORITY)

IMPORTANT: If the project has components.json (shadcn/ui installed), ALWAYS apply the shadcn theme as the FIRST customization step. This ensures Clerk components visually match the existing shadcn design system. Skip this only if the user explicitly requests a different theme.

If the project uses shadcn/ui (check for components.json in the project root), always use the shadcn theme:

import { shadcn } from '@clerk/ui/themes'

<ClerkProvider appearance={{ theme: shadcn }} />

Also import shadcn CSS in your global styles:

@import 'tailwindcss';
@import '@clerk/ui/themes/shadcn.css';

Core 2 ONLY (skip if current SDK): Import from @clerk/themes and @clerk/themes/shadcn.css:

import { shadcn } from '@clerk/themes'

@import '@clerk/themes/shadcn.css';

Workflow

1. Identify customization needs (custom flow or appearance)
2. For custom flows: check SDK version → read appropriate core-2/ or core-3/ reference
3. For appearance: WebFetch the appropriate documentation from table above
4. Apply appearance prop to your Clerk components or build custom flow with hooks

Common Pitfalls

Issue	Solution
Colors not applying	Use colorPrimary not primaryColor
Logo not showing	Put logoImageUrl inside options: {} (or layout: {} in Core 2)
Social buttons wrong	Add socialButtonsVariant: 'iconButton' in options (or layout in Core 2)
Styling not working	Use appearance prop, not direct CSS (unless with bring-your-own-css)
Hook returns different shape	Check SDK version — Core 2 and current have completely different useSignIn/useSignUp APIs