:root {
    /* Brand Colors - Modern & Minimalist Palette */
    --color-primary: #4A90E2;           /* Vibrant blue - trust, learning, sky */
    --color-primary-dark: #357ABD;      /* Darker blue for hover states */
    --color-primary-light: #7EB3F1;     /* Light blue for backgrounds */
    --color-primary-subtle: #E8F4FD;    /* Very light blue for cards */

    --color-secondary: #50C878;         /* Emerald green - growth, success */
    --color-accent: #FFB84D;            /* Warm orange - joy, energy */

    /* Neutral Colors */
    --color-white: #FFFFFF;
    --color-gray-50: #F9FAFB;
    --color-gray-100: #F3F4F6;
    --color-gray-200: #E5E7EB;
    --color-gray-300: #D1D5DB;
    --color-gray-400: #9CA3AF;
    --color-gray-500: #6B7280;
    --color-gray-600: #4B5563;
    --color-gray-700: #374151;
    --color-gray-800: #1F2937;
    --color-gray-900: #111827;

    /* Semantic Colors */
    --color-success: #10B981;
    --color-error: #EF4444;
    --color-warning: #F59E0B;
    --color-info: #3B82F6;

    /* Background */
    --color-background: #FFFFFF;
    --color-surface: #F9FAFB;
    --color-card: #FFFFFF;
    --color-input-background: #FFFFFF;
    --color-input-border: var(--color-gray-300);
    --color-focus-ring: rgba(74, 144, 226, 0.2);

    /* Auth Surface Colors */
    --color-auth-gradient-start: #667EEA;
    --color-auth-gradient-end: #764BA2;
    --color-auth-heading: #1A202C;
    --color-auth-body: #718096;
    --color-auth-label: #2D3748;
    --color-auth-link: #667EEA;
    --color-auth-link-hover: #764BA2;
    --color-auth-button-shadow: rgba(102, 126, 234, 0.4);
    --color-spinner-track: rgba(255, 255, 255, 0.3);
    --color-spinner-head: #FFFFFF;
    --color-loading-spinner-track: #E2E8F0;
    --color-loading-spinner-head: #667EEA;

    /* Alert Colors */
    --color-alert-success-bg: #C6F6D5;
    --color-alert-success-text: #22543D;
    --color-alert-success-border: #9AE6B4;
    --color-alert-error-bg: #FED7D7;
    --color-alert-error-text: #742A2A;
    --color-alert-error-border: #FC8181;
    --color-alert-info-bg: #BEE3F8;
    --color-alert-info-text: #2C5282;
    --color-alert-info-border: #90CDF4;
    --color-alert-warning-bg: #FEEBC8;
    --color-alert-warning-text: #7C2D12;
    --color-alert-warning-border: #FBD38D;

    /* Typography */
    --font-family-primary: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
    --font-family-heading: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;

    --font-size-xs: 0.75rem;      /* 12px */
    --font-size-sm: 0.875rem;     /* 14px */
    --font-size-base: 1rem;       /* 16px */
    --font-size-lg: 1.125rem;     /* 18px */
    --font-size-xl: 1.25rem;      /* 20px */
    --font-size-2xl: 1.5rem;      /* 24px */
    --font-size-3xl: 1.875rem;    /* 30px */
    --font-size-4xl: 2.25rem;     /* 36px */
    --font-size-5xl: 3rem;        /* 48px */

    --font-weight-normal: 400;
    --font-weight-medium: 500;
    --font-weight-semibold: 600;
    --font-weight-bold: 700;

    --line-height-tight: 1.25;
    --line-height-normal: 1.5;
    --line-height-relaxed: 1.75;

    /* Spacing */
    --spacing-xs: 0.25rem;        /* 4px */
    --spacing-sm: 0.5rem;         /* 8px */
    --spacing-md: 1rem;           /* 16px */
    --spacing-lg: 1.5rem;         /* 24px */
    --spacing-xl: 2rem;           /* 32px */
    --spacing-2xl: 3rem;          /* 48px */
    --spacing-3xl: 4rem;          /* 64px */
    --spacing-4xl: 6rem;          /* 96px */

    /* Border Radius */
    --radius-sm: 0.25rem;         /* 4px */
    --radius-md: 0.5rem;          /* 8px */
    --radius-lg: 0.75rem;         /* 12px */
    --radius-xl: 1rem;            /* 16px */
    --radius-full: 9999px;

    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);

    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-base: 200ms ease-in-out;
    --transition-slow: 300ms ease-in-out;

    /* Z-index layers */
    --z-base: 0;
    --z-dropdown: 1000;
    --z-sticky: 1100;
    --z-modal: 1200;
    --z-tooltip: 1300;

    /* Container widths */
    --container-sm: 640px;
    --container-md: 768px;
    --container-lg: 1024px;
    --container-xl: 1280px;
}

:root[data-theme="dark"] {
    --color-primary-subtle: rgba(74, 144, 226, 0.2);

    --color-gray-50: #111827;
    --color-gray-100: #1F2937;
    --color-gray-200: #374151;
    --color-gray-300: #4B5563;
    --color-gray-400: #6B7280;
    --color-gray-500: #9CA3AF;
    --color-gray-600: #D1D5DB;
    --color-gray-700: #E5E7EB;
    --color-gray-800: #F3F4F6;
    --color-gray-900: #F9FAFB;

    --color-background: #0B1220;
    --color-surface: #111827;
    --color-card: #1F2937;
    --color-input-background: #111827;
    --color-input-border: #4B5563;
    --color-focus-ring: rgba(126, 179, 241, 0.35);

    --color-auth-gradient-start: #1E293B;
    --color-auth-gradient-end: #0F172A;
    --color-auth-heading: #F3F4F6;
    --color-auth-body: #CBD5E1;
    --color-auth-label: #E2E8F0;
    --color-auth-link: #93C5FD;
    --color-auth-link-hover: #BFDBFE;
    --color-auth-button-shadow: rgba(30, 41, 59, 0.6);
    --color-spinner-track: rgba(148, 163, 184, 0.4);
    --color-spinner-head: #F8FAFC;
    --color-loading-spinner-track: #334155;
    --color-loading-spinner-head: #93C5FD;

    --color-alert-success-bg: #14532D;
    --color-alert-success-text: #BBF7D0;
    --color-alert-success-border: #166534;
    --color-alert-error-bg: #7F1D1D;
    --color-alert-error-text: #FECACA;
    --color-alert-error-border: #991B1B;
    --color-alert-info-bg: #1E3A8A;
    --color-alert-info-text: #BFDBFE;
    --color-alert-info-border: #1D4ED8;
    --color-alert-warning-bg: #78350F;
    --color-alert-warning-text: #FDE68A;
    --color-alert-warning-border: #92400E;

    --shadow-sm: 0 1px 3px 0 rgba(0, 0, 0, 0.35);
    --shadow-md: 0 4px 12px -2px rgba(0, 0, 0, 0.45);
    --shadow-lg: 0 12px 20px -6px rgba(0, 0, 0, 0.5);
    --shadow-xl: 0 20px 30px -10px rgba(0, 0, 0, 0.55);
}