/* Math Help - Design System Following Dieter Rams' Principles */

/* ===== DESIGN TOKENS ===== */
:root {
    /* Colors - Honest, purposeful palette */
    --color-primary: #2c3e50;      /* Deep, trustworthy blue-grey */
    --color-secondary: #34495e;    /* Supporting dark grey */
    --color-accent: #3498db;       /* Clear, functional blue */
    --color-success: #27ae60;      /* Natural green for positive actions */
    --color-warning: #f39c12;      /* Amber for caution */
    --color-error: #e74c3c;        /* Clear red for errors */
    
    /* Neutral scales - Thorough attention to detail */
    --color-white: #ffffff;
    --color-grey-50: #f8f9fa;
    --color-grey-100: #e9ecef;
    --color-grey-200: #dee2e6;
    --color-grey-300: #ced4da;
    --color-grey-400: #adb5bd;
    --color-grey-500: #6c757d;
    --color-grey-600: #495057;
    --color-grey-700: #343a40;
    --color-grey-800: #212529;
    --color-black: #000000;
    
    /* Typography - Clear hierarchy, maximum legibility */
    --font-family-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-family-mono: 'SF Mono', Monaco, 'Cascadia Code', 'Roboto Mono', Consolas, 'Courier New', monospace;
    
    --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 - Mathematical precision */
    --space-1: 0.25rem;   /* 4px */
    --space-2: 0.5rem;    /* 8px */
    --space-3: 0.75rem;   /* 12px */
    --space-4: 1rem;      /* 16px */
    --space-5: 1.25rem;   /* 20px */
    --space-6: 1.5rem;    /* 24px */
    --space-8: 2rem;      /* 32px */
    --space-10: 2.5rem;   /* 40px */
    --space-12: 3rem;     /* 48px */
    --space-16: 4rem;     /* 64px */
    --space-20: 5rem;     /* 80px */
    
    /* Layout - Logical constraints */
    --container-sm: 640px;
    --container-md: 768px;
    --container-lg: 1024px;
    --container-xl: 1280px;
    --container-2xl: 1536px;
    
    /* Effects - Subtle, purposeful */
    --border-radius-sm: 0.125rem;
    --border-radius: 0.25rem;
    --border-radius-md: 0.375rem;
    --border-radius-lg: 0.5rem;
    --border-radius-xl: 0.75rem;
    
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px 0 rgba(0, 0, 0, 0.06);
    --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);
    
    --transition-fast: 0.15s ease-out;
    --transition-normal: 0.2s ease-out;
    --transition-slow: 0.3s ease-out;
}

/* ===== RESET & BASE ===== */
/* Principle 10: As little design as possible - Clean foundation */
*, *::before, *::after {
    box-sizing: border-box;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
    -webkit-text-size-adjust: 100%;
}

body {
    margin: 0;
    font-family: var(--font-family-sans);
    font-size: var(--font-size-base);
    font-weight: var(--font-weight-normal);
    line-height: var(--line-height-normal);
    color: var(--color-grey-800);
    background-color: var(--color-white);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* ===== TYPOGRAPHY ===== */
/* Principle 4: Makes product understandable - Clear hierarchy */
h1, h2, h3, h4, h5, h6 {
    margin: 0 0 var(--space-4) 0;
    font-weight: var(--font-weight-semibold);
    line-height: var(--line-height-tight);
    color: var(--color-primary);
}

h1 { font-size: var(--font-size-4xl); }
h2 { font-size: var(--font-size-3xl); }
h3 { font-size: var(--font-size-2xl); }
h4 { font-size: var(--font-size-xl); }
h5 { font-size: var(--font-size-lg); }
h6 { font-size: var(--font-size-base); }

p {
    margin: 0 0 var(--space-4) 0;
    line-height: var(--line-height-relaxed);
}

a {
    color: var(--color-accent);
    text-decoration: none;
    transition: color var(--transition-normal);
}

a:hover {
    color: #2980b9;
    text-decoration: underline;
}

/* ===== LAYOUT COMPONENTS ===== */
/* Principle 2: Makes product useful - Functional structure */
.container {
    width: 100%;
    max-width: var(--container-xl);
    margin: 0 auto;
    padding: 0 var(--space-4);
}

.container-sm { max-width: var(--container-sm); }
.container-md { max-width: var(--container-md); }
.container-lg { max-width: var(--container-lg); }
.container-xl { max-width: var(--container-xl); }

/* Grid System */
.grid {
    display: grid;
    gap: var(--space-6);
}

.grid-cols-1 { grid-template-columns: repeat(1, minmax(0, 1fr)); }
.grid-cols-2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid-cols-3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid-cols-4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }

/* Flexbox utilities */
.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.gap-2 { gap: var(--space-2); }
.gap-4 { gap: var(--space-4); }
.gap-6 { gap: var(--space-6); }

/* ===== HEADER & NAVIGATION ===== */
/* Principle 5: Unobtrusive - Clear but not dominating */
.site-header {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 100%);
    color: var(--color-white);
    padding: var(--space-12) 0;
    text-align: center;
}

.site-title {
    font-size: var(--font-size-5xl);
    font-weight: var(--font-weight-bold);
    margin: 0 0 var(--space-2) 0;
    letter-spacing: -0.025em;
}

.tagline {
    font-size: var(--font-size-xl);
    font-weight: var(--font-weight-normal);
    opacity: 0.9;
    margin: 0;
}

.main-nav {
    background-color: var(--color-primary);
    border-bottom: 1px solid var(--color-secondary);
    position: sticky;
    top: 0;
    z-index: 50;
}

.nav-list {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
}

.nav-link {
    display: block;
    padding: var(--space-4) var(--space-5);
    color: var(--color-white);
    text-decoration: none;
    font-weight: var(--font-weight-medium);
    transition: background-color var(--transition-normal);
    border-bottom: 2px solid transparent;
}

.nav-link:hover,
.nav-link.active {
    background-color: var(--color-accent);
    border-bottom-color: rgba(255, 255, 255, 0.3);
    color: var(--color-white);
}

/* ===== BUTTONS & INTERACTIVE ELEMENTS ===== */
/* Principle 6: Honest - Clear about capabilities */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--space-3) var(--space-6);
    font-size: var(--font-size-base);
    font-weight: var(--font-weight-medium);
    line-height: 1;
    text-decoration: none;
    border: 1px solid transparent;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: all var(--transition-normal);
    min-height: 44px; /* Touch target */
    background: none;
}

.btn-primary,
.cta-button.primary {
    background-color: var(--color-accent);
    color: var(--color-white);
    border-color: var(--color-accent);
}

.btn-primary:hover,
.cta-button.primary:hover {
    background-color: #2980b9;
    border-color: #2980b9;
    color: var(--color-white);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-secondary,
.cta-button.secondary {
    background-color: transparent;
    color: var(--color-accent);
    border-color: var(--color-accent);
}

.btn-secondary:hover,
.cta-button.secondary:hover {
    background-color: var(--color-accent);
    color: var(--color-white);
}

.btn-ghost {
    background-color: transparent;
    color: var(--color-grey-600);
    border-color: var(--color-grey-300);
}

.btn-ghost:hover {
    background-color: var(--color-grey-50);
    color: var(--color-grey-800);
}

/* ===== CARDS & CONTENT CONTAINERS ===== */
/* Principle 3: Aesthetic - Pleasant to live with */
.card {
    background-color: var(--color-white);
    border: 1px solid var(--color-grey-200);
    border-radius: var(--border-radius-lg);
    padding: var(--space-6);
    box-shadow: var(--shadow-sm);
    transition: box-shadow var(--transition-normal);
}

.card:hover {
    box-shadow: var(--shadow-md);
}

.card-header {
    margin-bottom: var(--space-4);
    padding-bottom: var(--space-4);
    border-bottom: 1px solid var(--color-grey-100);
}

.card-title {
    font-size: var(--font-size-lg);
    font-weight: var(--font-weight-semibold);
    margin: 0;
    color: var(--color-primary);
}

.card-description {
    color: var(--color-grey-600);
    margin: var(--space-2) 0 0 0;
}

/* Topic Cards */
.topic-card {
    background: var(--color-white);
    border: 1px solid var(--color-grey-200);
    border-radius: var(--border-radius-lg);
    padding: var(--space-6);
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-sm);
}

.topic-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.topic-card.featured {
    border-color: var(--color-accent);
    border-width: 2px;
}

.topic-icon {
    font-size: var(--font-size-4xl);
    margin-bottom: var(--space-4);
    text-align: center;
}

.topic-card h3 {
    margin-bottom: var(--space-3);
    color: var(--color-primary);
}

.topic-highlights {
    list-style: none;
    padding: 0;
    margin: var(--space-4) 0;
}

.topic-highlights li {
    padding: var(--space-2) 0;
    border-bottom: 1px solid var(--color-grey-100);
}

.topic-highlights li:last-child {
    border-bottom: none;
}

.topic-highlights a {
    color: var(--color-grey-600);
    text-decoration: none;
    transition: color var(--transition-normal);
}

.topic-highlights a:hover {
    color: var(--color-accent);
}

.topic-link {
    display: inline-flex;
    align-items: center;
    color: var(--color-accent);
    font-weight: var(--font-weight-medium);
    text-decoration: none;
    margin-top: var(--space-4);
    transition: transform var(--transition-normal);
}

.topic-link:hover {
    transform: translateX(4px);
}

/* ===== MATHEMATICAL CONTENT ===== */
/* Principle 8: Thorough to last detail - Special math formatting */
.math-expression {
    font-family: var(--font-family-mono);
    background-color: var(--color-grey-50);
    padding: var(--space-2) var(--space-3);
    border-radius: var(--border-radius);
    border-left: 3px solid var(--color-accent);
    margin: var(--space-4) 0;
    overflow-x: auto;
}

.calculator-widget,
.calculator {
    background-color: var(--color-white);
    border: 2px solid var(--color-grey-200);
    border-radius: var(--border-radius-lg);
    padding: var(--space-6);
    max-width: 400px;
    margin: 0 auto;
    box-shadow: var(--shadow);
}

.calc-display {
    background-color: var(--color-grey-800);
    color: var(--color-white);
    padding: var(--space-4);
    border-radius: var(--border-radius);
    margin-bottom: var(--space-4);
    text-align: right;
    font-family: var(--font-family-mono);
    font-size: var(--font-size-xl);
    min-height: 60px;
    display: flex;
    align-items: center;
    justify-content: flex-end;
}

.calc-display input {
    background: transparent;
    border: none;
    color: var(--color-white);
    font-family: var(--font-family-mono);
    font-size: var(--font-size-xl);
    text-align: right;
    width: 100%;
    outline: none;
}

.calc-buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--space-2);
}

.calc-btn,
.calc-buttons button {
    background-color: var(--color-grey-100);
    border: 1px solid var(--color-grey-300);
    border-radius: var(--border-radius);
    padding: var(--space-4);
    font-size: var(--font-size-lg);
    font-weight: var(--font-weight-medium);
    cursor: pointer;
    transition: all var(--transition-fast);
    min-height: 50px;
}

.calc-btn:hover,
.calc-buttons button:hover {
    background-color: var(--color-grey-200);
    transform: translateY(-1px);
}

.calc-btn:active,
.calc-buttons button:active {
    transform: translateY(0);
}

.calc-btn.operator {
    background-color: var(--color-accent);
    color: var(--color-white);
    border-color: var(--color-accent);
}

.calc-btn.equals {
    background-color: var(--color-success);
    color: var(--color-white);
    border-color: var(--color-success);
}

/* Special calculator button layouts */
.calc-buttons button.zero {
    grid-column: span 2;
}

.calc-buttons button.equals {
    grid-row: span 2;
    background-color: var(--color-success);
    color: var(--color-white);
    border-color: var(--color-success);
}

/* ===== SECTIONS ===== */
.hero-section {
    padding: var(--space-16) 0;
    text-align: center;
    background: linear-gradient(135deg, var(--color-grey-50) 0%, var(--color-white) 100%);
}

.hero-content h1 {
    font-size: var(--font-size-4xl);
    margin-bottom: var(--space-4);
}

.hero-content p {
    font-size: var(--font-size-lg);
    color: var(--color-grey-600);
    max-width: 600px;
    margin: 0 auto var(--space-8) auto;
}

.hero-actions {
    display: flex;
    justify-content: center;
    gap: var(--space-4);
    flex-wrap: wrap;
    margin-bottom: var(--space-12);
}

.hero-stats {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-8);
    max-width: 600px;
    margin: 0 auto;
}

.stat-item {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: var(--font-size-3xl);
    font-weight: var(--font-weight-bold);
    color: var(--color-accent);
    margin-bottom: var(--space-2);
}

.stat-label {
    color: var(--color-grey-600);
    font-size: var(--font-size-sm);
}

.featured-topics,
.featured-examples,
.quick-access,
.learning-paths {
    padding: var(--space-16) 0;
}

.featured-topics h2,
.featured-examples h2,
.quick-access h2,
.learning-paths h2 {
    text-align: center;
    margin-bottom: var(--space-12);
}

.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--space-6);
    margin-bottom: var(--space-8);
}

/* ===== FOOTER ===== */
.site-footer {
    background-color: var(--color-grey-800);
    color: var(--color-white);
    padding: var(--space-12) 0;
    text-align: center;
}

.footer-links {
    margin-top: var(--space-4);
    display: flex;
    justify-content: center;
    gap: var(--space-6);
    flex-wrap: wrap;
}

.footer-links a {
    color: var(--color-grey-300);
    text-decoration: none;
    transition: color var(--transition-normal);
}

.footer-links a:hover {
    color: var(--color-white);
}

/* ===== RESPONSIVE DESIGN ===== */
/* Principle 7: Long-lasting - Works across all devices */
@media (max-width: 768px) {
    .container {
        padding: 0 var(--space-3);
    }
    
    .site-title {
        font-size: var(--font-size-3xl);
    }
    
    .tagline {
        font-size: var(--font-size-lg);
    }
    
    .nav-list {
        flex-direction: column;
    }
    
    .nav-link {
        text-align: center;
        border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    }
    
    .grid-cols-2,
    .grid-cols-3,
    .grid-cols-4 {
        grid-template-columns: 1fr;
    }
    
    .topics-grid {
        grid-template-columns: 1fr;
    }
    
    .hero-actions {
        flex-direction: column;
        align-items: center;
    }
    
    .hero-stats {
        grid-template-columns: 1fr;
        gap: var(--space-4);
    }
    
    .calc-buttons {
        gap: var(--space-3);
    }
    
    .calc-btn {
        min-height: 60px;
        font-size: var(--font-size-xl);
    }
}

@media (max-width: 480px) {
    .site-header {
        padding: var(--space-8) 0;
    }
    
    .site-title {
        font-size: var(--font-size-2xl);
    }
    
    .tagline {
        font-size: var(--font-size-base);
    }
    
    .hero-section {
        padding: var(--space-12) 0;
    }
    
    .hero-content h1 {
        font-size: var(--font-size-2xl);
    }
    
    .featured-topics,
    .featured-examples,
    .quick-access,
    .learning-paths {
        padding: var(--space-12) 0;
    }
}

/* ===== UTILITIES ===== */
/* Principle 9: Environmentally friendly - Efficient classes */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.font-mono { font-family: var(--font-family-mono); }
.font-medium { font-weight: var(--font-weight-medium); }
.font-semibold { font-weight: var(--font-weight-semibold); }
.font-bold { font-weight: var(--font-weight-bold); }

.text-primary { color: var(--color-primary); }
.text-secondary { color: var(--color-secondary); }
.text-accent { color: var(--color-accent); }
.text-success { color: var(--color-success); }
.text-warning { color: var(--color-warning); }
.text-error { color: var(--color-error); }
.text-muted { color: var(--color-grey-600); }

.bg-primary { background-color: var(--color-primary); }
.bg-secondary { background-color: var(--color-secondary); }
.bg-accent { background-color: var(--color-accent); }
.bg-grey-50 { background-color: var(--color-grey-50); }
.bg-white { background-color: var(--color-white); }

.border { border: 1px solid var(--color-grey-200); }
.border-0 { border: none; }
.rounded { border-radius: var(--border-radius); }
.rounded-lg { border-radius: var(--border-radius-lg); }

.shadow { box-shadow: var(--shadow); }
.shadow-md { box-shadow: var(--shadow-md); }
.shadow-lg { box-shadow: var(--shadow-lg); }

/* Spacing utilities */
.m-0 { margin: 0; }
.m-2 { margin: var(--space-2); }
.m-4 { margin: var(--space-4); }
.m-6 { margin: var(--space-6); }
.m-8 { margin: var(--space-8); }

.p-0 { padding: 0; }
.p-2 { padding: var(--space-2); }
.p-4 { padding: var(--space-4); }
.p-6 { padding: var(--space-6); }
.p-8 { padding: var(--space-8); }

.mt-4 { margin-top: var(--space-4); }
.mb-4 { margin-bottom: var(--space-4); }
.ml-4 { margin-left: var(--space-4); }
.mr-4 { margin-right: var(--space-4); }

.pt-4 { padding-top: var(--space-4); }
.pb-4 { padding-bottom: var(--space-4); }
.pl-4 { padding-left: var(--space-4); }
.pr-4 { padding-right: var(--space-4); }

/* ===== LOADING & STATES ===== */
.loading {
    display: inline-flex;
    align-items: center;
    gap: var(--space-2);
    color: var(--color-grey-600);
}

.loading::before {
    content: '';
    width: 16px;
    height: 16px;
    border: 2px solid var(--color-grey-300);
    border-top-color: var(--color-accent);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Focus styles for accessibility */
.btn:focus,
.calc-btn:focus,
.nav-link:focus {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
}

/* Print styles */
@media print {
    .nav-link,
    .btn,
    .calc-buttons {
        color-adjust: exact;
    }
}

/* ===== AD CONTAINER STYLES (UNOBTRUSIVE) ===== */
/* Following principle 5: Unobtrusive design */
.ad-container {
    margin: var(--space-8) 0;
    text-align: center;
    border-top: 1px solid var(--color-grey-100);
    border-bottom: 1px solid var(--color-grey-100);
    padding: var(--space-4) 0;
}

.ad-container::before {
    content: 'Advertisement';
    display: block;
    font-size: var(--font-size-xs);
    color: var(--color-grey-400);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-2);
}

/* ===== MOBILE TOOLS ===== */
.mobile-tools {
    display: none;
    background: var(--color-grey-50);
    padding: var(--space-4) 0;
    border-top: 1px solid var(--color-grey-200);
}

.mobile-tools-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: var(--space-2);
}

.mobile-tool-btn {
    background: var(--color-accent);
    color: var(--color-white);
    border: none;
    padding: var(--space-3) var(--space-2);
    border-radius: var(--border-radius);
    font-size: var(--font-size-sm);
    text-decoration: none;
    display: block;
    text-align: center;
    transition: background-color var(--transition-normal);
}

.mobile-tool-btn:hover {
    background-color: #2980b9;
    color: var(--color-white);
}

@media (max-width: 768px) {
    .mobile-tools {
        display: block;
    }
}