igniteui-wc-customize-component-theme

name: igniteui-wc-customize-component-theme description: Customize Ignite UI Web Components styling using CSS custom properties, optional Sass, and the igniteui-theming MCP server for AI-assisted theming user-invocable: true

Ignite UI Web Components — Theming Skill

Description

This skill teaches AI agents how to theme Ignite UI Web Components (and React via igniteui-react) applications. Two approaches are supported:

• CSS custom properties — works in any project without additional build tooling
• Sass — available when the project has Sass configured; provides the full palette/typography/elevation API

The skill also covers component-level theming, layout controls (spacing, sizing, roundness), and how to use the Ignite UI Theming MCP server for AI-assisted code generation.

Prerequisites

• A project with igniteui-webcomponents (or igniteui-react) installed
• The Ignite UI Theming MCP server (igniteui-theming) available as a tool provider
• Optional: Sass configured in the project (enables the Sass-based theming API)

AGENT INSTRUCTION — MCP Server Setup (REQUIRED)

Before using any theming tools, you MUST verify the MCP server is available by calling detect_platform. If the tool is not available or the call fails, you MUST automatically configure it by following the setup process steps described below.

After writing the file, inform the user that the MCP server has been configured and they may need to reload the editor for the tools to activate. Start the MCP server and wait for that MCP server to start before continuing the theming related work. Do NOT skip this step or ask the user to do it manually.

Setting Up the Theming MCP Server

See references/mcp-setup.md for VS Code, Cursor, Claude Desktop, and WebStorm configuration instructions.

Verify the server is running by calling detect_platform — it reads your package.json and returns the detected platform (e.g., webcomponents).

Theming Architecture

The theming system is built on four pillars:

Four built-in design systems are available — each with light and dark variants:

For the full live reference (palette families, design system schemas, variant constraints, and preset palettes) call:

read_resource({ uri: "theming://platforms/webcomponents" })

Additional guidance resources:

• read_resource({ uri: "theming://guidance/colors/roles" }) — which components use primary vs secondary vs surface, and which shade (50/500/900) to use where
• read_resource({ uri: "theming://guidance/colors/rules" }) — surface and gray luminance rules for light/dark variants (why gray is inverted from surface, WCAG contrast thresholds)

Pre-built Themes

The quickest way to theme an app is to import a pre-built CSS file in your entry point:

import 'igniteui-webcomponents/themes/light/bootstrap.css';

Available pre-built CSS files:

Custom Theme via CSS Custom Properties

No Sass required. Works in any project after importing a pre-built theme.

After importing a pre-built theme, override the *-500 base shade to change a color family. All other shades (50–900) derive from the 500 value automatically via CSS relative color syntax:

:root {
  /* Override the 500 (base) shade — all other shades update automatically */
  --ig-primary-500: #1976D2;
  --ig-secondary-500: #FF9800;
}

To scope overrides to a specific container:

.admin-panel {
  --ig-primary-500: #6200EA;
}

For dark mode, either import a dark theme CSS file directly or toggle overrides with a class or media query:

@media (prefers-color-scheme: dark) {
  :root {
    --ig-surface-500: #121212;
    --ig-primary-500: #90CAF9; /* lighter tint works better on dark backgrounds */
  }
}

/* Or manually with a class */
.dark-theme {
  --ig-surface-500: #222;
}

Custom Theme via Sass

Requires Sass configured in the project. First check whether the project has a Sass setup (e.g., a styles.scss entry file, sass in devDependencies, or a Vite/webpack Sass plugin).

The Sass API for igniteui-webcomponents uses @use 'igniteui-theming' with individual mixins — not the Angular-specific core() / theme() combined mixins.

Call create_theme to generate production-ready Sass for palette + typography + elevations in a single step:

create_theme({
  platform: "webcomponents",
  designSystem: "material",    // or "bootstrap", "fluent", "indigo"
  primaryColor: "#1976D2",
  secondaryColor: "#FF9800",
  surfaceColor: "#FAFAFA",
  variant: "light",
  fontFamily: "'Roboto', sans-serif",
  includeTypography: true,
  includeElevations: true
})

For a dark theme pass a dark surfaceColor (e.g. "#121212") and variant: "dark" — create_theme selects the correct dark schema automatically.

For palette-only generation (when typography/elevations are already set) use create_palette. For scoping a theme to a container, pass the generated @include palette(...) block inside the target selector.

Component-Level Theming

Override individual component appearance using component theme functions and the tokens mixin.

AGENT INSTRUCTION — No Hardcoded Colors (CRITICAL)

Once a palette has been generated (via palette() in Sass or create_palette / create_theme via MCP), every color reference MUST come from the generated palette tokens — never hardcode hex/RGB/HSL values.

Use var(--ig-primary-500), var(--ig-secondary-300), var(--ig-surface-500), etc. in CSS, or the get_color MCP tool to obtain the correct token reference.

WRONG (hardcoded hex — breaks theme switching, ignores the palette):

igc-avatar {
  --ig-avatar-background: #E91E63;  /* ✗ hardcoded */
  --ig-avatar-color: #FFFFFF;       /* ✗ hardcoded */
}

RIGHT — CSS (palette token — stays in sync with the theme):

igc-avatar {
  --ig-avatar-background: var(--ig-primary-500);
  --ig-avatar-color: var(--ig-primary-500-contrast);
}

RIGHT — Sass (when Sass is configured):

$custom-avatar: avatar-theme(
  $schema: $light-material-schema,
  $background: var(--ig-primary-500),
  $color: var(--ig-primary-500-contrast)
);

This applies to all style code: component themes, custom CSS rules, and inline styles. The only place raw hex values belong is the initial palette() call that seeds the color system. Everything downstream must reference the palette.

igc-avatar {
  --ig-avatar-background: var(--ig-primary-500);
  --ig-avatar-color: var(--ig-primary-500-contrast);
}

When Sass is configured, use create_component_theme to generate the correct avatar-theme(...) + @include tokens(...) block:

create_component_theme({
  platform: "webcomponents",
  component: "avatar",
  tokens: { "background": "var(--ig-primary-500)", "color": "var(--ig-primary-500-contrast)" }
})

Pass output: "css" if you want CSS custom properties instead of Sass.

Discovering Available Tokens

Each component has its own set of design tokens (themeable CSS custom properties). Before theming a component, you must know which tokens exist. Use the MCP tool get_component_design_tokens to discover them.

Compound Components

Some components (e.g., combo, grid, date-picker, select) are compound — they contain internal child components, each requiring their own theme. For example, date-picker uses calendar, flat-button, and input-group internally.

Workflow for compound components:

1. Call get_component_design_tokens for the parent (e.g., date-picker)
2. The response lists related themes and scope selectors
3. Call create_component_theme for each child, using the parent's selector as the wrapper

Layout Controls

Use the MCP layout tools to generate the correct CSS or Sass output:

set_size({ size: "medium" })                              // global, CSS
set_size({ size: "small", component: "grid" })            // component-scoped, CSS
set_size({ size: "medium", output: "sass" })              // Sass output

set_spacing({ spacing: 0.75 })                            // compact, global
set_spacing({ spacing: 0.75, component: "grid" })         // component-scoped

set_roundness({ radiusFactor: 0.5 })                      // global
set_roundness({ radiusFactor: 0.0 })                      // square

All three tools default to CSS output. Add output: "sass" when the project has Sass configured.

The underlying CSS custom properties are --ig-size, --ig-spacing, and --ig-radius-factor. You can also set them directly on :root or a scoped selector if a one-off override is simpler than a tool call.

Using the Theming MCP Server

The Ignite UI Theming MCP server provides tools for AI-assisted theme code generation.

IMPORTANT — File Safety Rule: When generating or updating theme code, never overwrite existing style files directly. Instead, always propose the changes as an update and let the user review and approve before writing to disk. If a styles.scss (or any target file) already exists, show the generated code as a diff or suggestion rather than replacing the file contents. This prevents accidental loss of custom styles the user has already written.

Quick tool sequence — for full parameter details, see earlier sections:

Loading Reference Data

Use read_resource with these URIs for preset values and documentation:

Referencing Colors in Custom Styles

After a theme is applied, the palette is available as CSS custom properties on :root. Use these tokens in all custom CSS — never introduce standalone hex/RGB variables for colors that the palette already provides.

Correct: Palette Tokens

/* All colors come from the theme — respects palette changes and dark/light switching */
.sidebar {
  background: var(--ig-surface-500);
  color: var(--ig-gray-900);
  border-right: 1px solid var(--ig-gray-200);
}

.accent-badge {
  background: var(--ig-secondary-500);
  color: var(--ig-secondary-500-contrast);
}

.hero-section {
  /* Semi-transparent primary overlay */
  background: hsl(from var(--ig-primary-500) h s l / 0.12);
}

Incorrect: Hardcoded Values

/* WRONG — these break when the palette changes and ignore dark/light mode */
.sidebar {
  background: #F0F5FA;  /* ✗ not a palette token */
  color: #333;          /* ✗ not a palette token */
}

When Raw Hex Values Are OK

Raw hex values are acceptable only in these contexts:

1. palette() call — the initial seed colors that generate the full palette
2. create_palette / create_theme MCP tool inputs — the base colors passed to the tool
3. Non-palette decorative values — e.g., a one-off SVG illustration color that intentionally stays fixed regardless of theme

Everything else must use var(--ig-<family>-<shade>) tokens.

Common Patterns

Switching Between Light and Dark Themes — CSS approach

Import the appropriate theme CSS and toggle with a class or media query:

// In your entry point — choose one variant as the default
import 'igniteui-webcomponents/themes/light/bootstrap.css';

/* Override surface base color for dark mode */
.dark-theme {
  --ig-surface-500: #121212;
}

@media (prefers-color-scheme: dark) {
  :root {
    --ig-surface-500: #121212;
    --ig-primary-500: #90CAF9; /* lighter tint works better on dark backgrounds */
  }
}

Or dynamically swap the stylesheet at runtime:

function setTheme(variant: 'light' | 'dark', design = 'bootstrap') {
  const link = document.getElementById('igc-theme') as HTMLLinkElement;
  link.href = `node_modules/igniteui-webcomponents/themes/${variant}/${design}.css`;
}

Switching Between Light and Dark Themes — Sass approach

When Sass is configured, generate both theme blocks with create_theme — once with variant: "light" and once with variant: "dark". Use the generated @include palette(...) call inside .dark-theme { } for the dark variant. The tool selects the correct schema automatically for each variant.

Scoping a Theme to a Container — CSS approach

.admin-panel {
  --ig-primary-500: #6200EA;
}

Scoping a Theme to a Container — Sass approach

Generate the palette block with create_palette and wrap it in the target container selector manually, or pass a custom selector when using create_component_theme for component-scoped overrides.

Key Rules

1. Never overwrite existing files directly — always propose theme code as an update for user review; do not replace existing style files without confirmation
2. Always call detect_platform first when using MCP tools
3. Always call get_component_design_tokens before create_component_theme to discover valid token names
4. Palette shades 50 = lightest, 900 = darkest for all chromatic colors — never invert for dark themes (only gray inverts)
5. Surface color must match the variant — light color for light, dark color for dark
6. Sass only: Use create_theme (or create_palette / create_typography / create_elevations individually) to generate correct Sass — the theming module for Web Components is igniteui-theming, not igniteui-angular/theming; Angular-specific core() / theme() combined mixins do not apply here
7. Sass only: Component themes use create_component_theme to generate @include tokens($theme) inside the correct selector
8. For compound components, follow the full checklist returned by get_component_design_tokens — theme each child component with its scoped selector
9. Never hardcode colors after palette generation — once a palette is created, every color in component themes, custom CSS, and Sass variables must use var(--ig-<family>-<shade>) palette tokens (e.g., var(--ig-primary-500), var(--ig-gray-200)). Raw hex/RGB/HSL values are only acceptable in the initial palette() seed call. This ensures themes remain consistent, switchable (light/dark), and maintainable