name: styling-architecture description: Use when working with CSS variables, theming, or colors. Triggers on "CSS variable", "theme", "dark mode", "light mode", "color token", "semantic color", "--background", "--foreground", "theme()", or color questions. allowed-tools:

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Styling Architecture & CSS Variables

This document defines our CSS architecture, color system, and styling patterns.

Color System

Principle: Tailwind Built-in Colors Only

We use only Tailwind's built-in zinc scale for all colors. No custom hex codes.

Tailwind Built-in Colors (zinc-50 to zinc-950)
  -> CSS Variables (semantic tokens via theme() function)
  -> Tailwind Utility Classes (bg-background, text-foreground)

Color Scale Reference

Zinc Level	Light Mode Usage	Dark Mode Usage
`zinc-50`	Background	Foreground/Text
`zinc-100`	Muted/Secondary	-
`zinc-200`	Borders (light)	-
`zinc-300`	Border hover	-
`zinc-400`	Ring/Focus	Muted text
`zinc-500`	Muted text	Muted text
`zinc-600`	-	Ring/Focus, Border hover
`zinc-700`	-	Borders
`zinc-800`	-	Muted/Accent
`zinc-900`	Primary, Cards	Cards
`zinc-950`	Foreground/Text	Background

CSS Variables

Location

All CSS variables are defined in one place: apps/demo/src/styles.css

Naming Convention

Variables follow Spartan UI conventions for compatibility:

--background          /* Page/app background */
--foreground          /* Primary text color */
--foreground-muted    /* Secondary/muted text */
--card                /* Card backgrounds */
--card-foreground     /* Card text */
--muted               /* Muted backgrounds */
--muted-foreground    /* Muted text */
--accent              /* Accent backgrounds (hover states) */
--accent-foreground   /* Accent text */
--border              /* Default border color */
--border-hover        /* Border on hover/focus */
--input               /* Input border color */
--ring                /* Focus ring color */
--primary             /* Primary button/action */
--primary-foreground  /* Primary button text */
--secondary           /* Secondary button/action */
--secondary-foreground /* Secondary button text */
--destructive         /* Destructive/danger color */
--destructive-foreground /* Destructive text */

Variable Definition Pattern

Always use theme() function to reference Tailwind colors:

/* Correct: Use theme() function */
--background: theme('colors.zinc.50');
--border: theme('colors.zinc.200');

/* Wrong: Never use hex codes */
--background: #fafafa;
--border: #e4e4e7;

/* Wrong: Never use rgb/hsl */
--background: rgb(250 250 250);

Using Variables in Components

In CSS/Templates

Use var() for CSS variable references:

/* In CSS */
.my-component {
  background-color: var(--card);
  border: 1px solid var(--border);
  color: var(--foreground);
}

In Tailwind Classes (Templates)

Use Tailwind semantic color classes directly:

<!-- Correct: Tailwind semantic color classes -->
<div class="border-border bg-card text-foreground">
  <div class="bg-muted text-muted-foreground">Muted content</div>
</div>

<!-- Wrong: var() syntax in Tailwind classes -->
<div class="border-[var(--border)] bg-[var(--card)]"></div>

<!-- Wrong: dark: prefix -->
<div class="bg-white text-gray-900 dark:bg-gray-900 dark:text-gray-100"></div>

<!-- Wrong: Hardcoded hex colors -->
<div class="border-[#3f3f46] bg-[#18181b]"></div>

In TypeScript (cn utility)

cardClasses = computed(() => {
  return cn(
    'rounded-lg',
    'border border-border',
    'bg-card',
    'text-foreground',
    'hover:border-border-hover'
  );
});

Light/Dark Mode

How It Works

Dark mode is controlled by the .dark class on <html>. CSS variables automatically switch values:

:root {
  --background: theme('colors.zinc.50'); /* Light */
  --foreground: theme('colors.zinc.950');
}

.dark {
  --background: theme('colors.zinc.950'); /* Dark */
  --foreground: theme('colors.zinc.50');
}

Component Pattern

Components automatically adapt via Tailwind semantic classes. NEVER use the dark: prefix.

// Correct: Tailwind semantic classes auto-switch light/dark
containerClasses = computed(() =>
  cn(
    'bg-background', // Auto-switches light/dark
    'text-foreground', // Auto-switches light/dark
    'border-border'
  )
);

// NEVER use dark: prefix
containerClasses = computed(() =>
  cn(
    'bg-white dark:bg-gray-900', // WRONG!
    'text-gray-900 dark:text-gray-100' // WRONG!
  )
);

Why No dark: Prefix?

CSS variables handle theme switching automatically
dark: prefix creates maintenance burden
Components become theme-aware without extra code
Single source of truth for colors in styles.css

Semantic Token Usage Guide

Backgrounds

Token	Use For
`--background`	Page/app background
`--card`	Card, modal, dialog backgrounds
`--popover`	Tooltip, dropdown backgrounds
`--muted`	Secondary/subtle backgrounds
`--accent`	Hover state backgrounds
`--primary`	Primary buttons
`--secondary`	Secondary buttons

Text Colors

Token	Use For
`--foreground`	Primary text
`--foreground-muted`	Secondary/hint text
`--muted-foreground`	Subtle text on muted bg
`--card-foreground`	Text on cards
`--accent-foreground`	Text on accent bg
`--primary-foreground`	Text on primary buttons

Borders

Token	Use For
`--border`	Default borders
`--border-hover`	Border on hover/focus
`--input`	Input field borders
`--ring`	Focus rings

What NOT to Do

NEVER Use dark: Prefix

// WRONG: dark: prefix
'bg-white dark:bg-gray-900';
'text-gray-900 dark:text-gray-100';
'border-gray-200 dark:border-gray-800';

// CORRECT: Tailwind semantic classes
'bg-card';
'text-foreground';
'border-border';

NEVER Use var() in Tailwind Classes

// WRONG: var() syntax
'bg-[var(--card)]';
'text-[var(--foreground)]';
'border-[var(--border)]';

// CORRECT: Tailwind semantic classes
'bg-card';
'text-foreground';
'border-border';

Never Use Hex Codes

/* Wrong */
--background: #09090b;
--border: #27272a;

/* Correct */
--background: theme('colors.zinc.950');
--border: theme('colors.zinc.800');

Never Create Custom Color Scales

/* Wrong: Custom color tokens */
--ai-blue-500: #3b82f6;
--ai-gray-800: #1f2937;

/* Correct: Use semantic tokens */
--primary: theme('colors.zinc.900');
--muted: theme('colors.zinc.800');

Quick Reference: Common Patterns

Card Component

cardClasses = computed(() =>
  cn(
    'rounded-lg',
    'border border-border',
    'bg-card',
    'shadow-sm',
    'hover:border-border-hover',
    'hover:shadow-md'
  )
);

Input Field

inputClasses = computed(() =>
  cn(
    'w-full rounded-md',
    'border border-input',
    'bg-transparent',
    'text-foreground',
    'placeholder:text-muted-foreground',
    'focus:border-ring',
    'focus:ring-1 focus:ring-ring'
  )
);

Muted Text

<span class="text-muted-foreground">Secondary info</span>

Button Variants

// Primary
'bg-primary text-primary-foreground';

// Secondary
'bg-secondary text-secondary-foreground';

// Ghost
'bg-transparent hover:bg-accent text-foreground';

Checklist: Before Committing CSS Changes

All colors use theme() function (no hex codes)
New variables added to both :root and .dark
Variables follow existing naming conventions
No duplicate variable definitions
Components use Tailwind semantic classes (bg-card, text-foreground, etc.)
NO dark: prefix used anywhere
NO var() syntax in Tailwind classes
Light and dark mode tested

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