/**
 * Main Stylesheet
 * 
 * Modern, responsive design with light/dark mode support
 * Mobile-first approach, optimized for performance
 * 
 * @package ChessTimerDigital
 * @version 1.0.0
 */

/* ============================================
   CSS VARIABLES (Theme Colors)
   ============================================ */

:root {
    /* Primary Colors */
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --primary-light: #3b82f6;
    
    /* Secondary Colors */
    --secondary-color: #10b981;
    --secondary-hover: #059669;
    
    /* Neutral Colors - Light Mode */
    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-tertiary: #f3f4f6;
    --text-primary: #111827;
    --text-secondary: #6b7280;
    --text-tertiary: #9ca3af;
    --border-color: #e5e7eb;
    --shadow-color: rgba(0, 0, 0, 0.1);
    
    /* Accent Colors */
    --success-color: #10b981;
    --error-color: #ef4444;
    --warning-color: #f59e0b;
    --info-color: #3b82f6;
    
    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-mono: 'Courier New', monospace;
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    --spacing-3xl: 4rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-full: 9999px;
    
    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-base: 300ms ease-in-out;
    --transition-slow: 500ms ease-in-out;
    
    /* 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);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    
    /* Z-index */
    --z-dropdown: 1000;
    --z-sticky: 1020;
    --z-fixed: 1030;
    --z-modal-backdrop: 1040;
    --z-modal: 1050;
    --z-popover: 1060;
    --z-tooltip: 1070;
}

/* Dark Mode Variables */
[data-theme="dark"] {
    --bg-primary: #111827;
    --bg-secondary: #1f2937;
    --bg-tertiary: #374151;
    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --text-tertiary: #9ca3af;
    --border-color: #374151;
    --shadow-color: rgba(0, 0, 0, 0.3);
}

/* ============================================
   RESET & BASE STYLES
   ============================================ */

*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-primary);
    font-size: 1rem;
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-primary);
    transition: background-color var(--transition-base), color var(--transition-base);
}

body.menu-open {
    overflow: hidden;
}

/* ============================================
   TYPOGRAPHY
   ============================================ */

h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.75rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.25rem; }
h6 { font-size: 1.125rem; }

@media (max-width: 768px) {
    h1 { font-size: 2rem; }
    h2 { font-size: 1.75rem; }
    h3 { font-size: 1.5rem; }
    h4 { font-size: 1.25rem; }
}

p {
    margin-bottom: var(--spacing-md);
    color: var(--text-secondary);
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color var(--transition-fast);
}

a:hover {
    color: var(--primary-hover);
}

strong, b {
    font-weight: 600;
}

/* ============================================
   LAYOUT
   ============================================ */

.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

.container-narrow {
    max-width: 900px;
}

.container-wide {
    max-width: 1400px;
}

/* ============================================
   HEADER
   ============================================ */

.site-header {
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: var(--z-sticky);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

.header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md) 0;
    gap: var(--spacing-lg);
}

.site-logo img {
    height: 40px;
    width: auto;
    display: block;
}

/* ============================================
   NAVIGATION
   ============================================ */

.main-navigation {
    display: flex;
    align-items: center;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: var(--spacing-sm);
    align-items: center;
}

.nav-item {
    position: relative;
}

.nav-link {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-sm) var(--spacing-md);
    color: var(--text-secondary);
    font-weight: 500;
    font-size: 0.9375rem;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.nav-link:hover {
    color: var(--primary-color);
    background: var(--bg-secondary);
}

.nav-item.active .nav-link {
    color: var(--primary-color);
    background: var(--bg-secondary);
}

.nav-icon {
    width: 18px;
    height: 18px;
}

/* Dropdown Menu */
.dropdown-menu {
    position: absolute;
    top: 100%;
    left: 0;
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    min-width: 200px;
    padding: var(--spacing-sm);
    opacity: 0;
    transform: translateY(-10px);
    transition: all var(--transition-base);
    pointer-events: none;
    z-index: var(--z-dropdown);
    display: none;
}

.dropdown-menu.active {
    opacity: 1;
    transform: translateY(0);
    pointer-events: all;
}

.dropdown-item {
    list-style: none;
}

.dropdown-link {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    color: var(--text-secondary);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
    font-size: 0.9375rem;
}

.dropdown-link:hover {
    color: var(--primary-color);
    background: var(--bg-secondary);
}

.dropdown-arrow {
    width: 12px;
    height: 12px;
    transition: transform var(--transition-fast);
}

.has-dropdown:hover .dropdown-arrow {
    transform: rotate(180deg);
}

/* Mobile Menu */
.mobile-menu-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--spacing-sm);
    width: 40px;
    height: 40px;
    flex-direction: column;
    justify-content: center;
    gap: 5px;
}

.hamburger-line {
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    border-radius: var(--radius-full);
    transition: all var(--transition-fast);
}

.mobile-menu {
    display: none;
}

.mobile-menu-overlay {
    display: none;
}

/* Mobile Responsive */
@media (max-width: 768px) {
    .desktop-menu {
        display: none;
    }
    
    .mobile-menu-toggle {
        display: flex;
    }
    
    .mobile-menu {
        position: fixed;
        top: 0;
        right: -100%;
        width: 280px;
        height: 100vh;
        background: var(--bg-primary);
        box-shadow: var(--shadow-xl);
        z-index: var(--z-modal);
        transition: right var(--transition-base);
        overflow-y: auto;
        display: flex;
        flex-direction: column;
        padding: 0;
    }
    
    .mobile-menu.active {
        right: 0;
    }
    
    .mobile-menu-overlay {
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100vh;
        background: rgba(0, 0, 0, 0.5);
        z-index: calc(var(--z-modal) - 1);
        opacity: 0;
        pointer-events: none;
        transition: opacity var(--transition-base);
        display: block;
    }
    
    .mobile-menu-overlay.active {
        opacity: 1;
        pointer-events: all;
    }
    
    .mobile-menu-header {
        display: flex;
        align-items: center;
        justify-content: space-between;
        padding: var(--spacing-lg);
        border-bottom: 1px solid var(--border-color);
    }
    
    .mobile-menu-title {
        font-weight: 700;
        font-size: 1.125rem;
        color: var(--text-primary);
    }
    
    .mobile-menu-close {
        background: none;
        border: none;
        cursor: pointer;
        padding: var(--spacing-xs);
        color: var(--text-secondary);
    }
    
    .mobile-menu .nav-item {
        border-bottom: 1px solid var(--border-color);
    }
    
    .mobile-menu .nav-link {
        padding: var(--spacing-md) var(--spacing-lg);
        border-radius: 0;
    }
    
    .mobile-menu .nav-link-sub {
        padding-left: var(--spacing-2xl);
        font-size: 0.875rem;
    }
    
    .mobile-menu .nav-link-small {
        font-size: 0.875rem;
        color: var(--text-tertiary);
    }
    
    .mobile-menu-divider {
        height: 1px;
        background: var(--border-color);
        margin: var(--spacing-md) 0;
    }
}

/* ============================================
   THEME TOGGLE
   ============================================ */

.theme-toggle {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: var(--spacing-sm);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    transition: all var(--transition-fast);
}

.theme-toggle:hover {
    background: var(--bg-tertiary);
}

.theme-toggle .sun-icon {
    display: block;
}

.theme-toggle .moon-icon {
    display: none;
}

[data-theme="dark"] .theme-toggle .sun-icon {
    display: none;
}

[data-theme="dark"] .theme-toggle .moon-icon {
    display: block;
}

/* ============================================
   MAIN CONTENT
   ============================================ */

.site-main {
    min-height: calc(100vh - 200px);
    padding: var(--spacing-2xl) 0;
}

/* Skip to Main Content Link (Accessibility) */
.skip-to-main {
    position: absolute;
    top: -100px;
    left: 0;
    background: var(--primary-color);
    color: white;
    padding: var(--spacing-md);
    z-index: 9999;
    transition: top var(--transition-fast);
}

.skip-to-main:focus {
    top: 0;
}

/* ============================================
   BUTTONS
   ============================================ */

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: 0.75rem 1.5rem;
    font-size: 1rem;
    font-weight: 600;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    text-decoration: none;
    font-family: inherit;
}

.btn-primary {
    background: var(--primary-color);
    color: white;
}

.btn-primary:hover {
    background: var(--primary-hover);
    color: white;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.btn-secondary:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

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

.btn-success:hover {
    background: #059669;
    color: white;
}

.btn-lg {
    padding: 1rem 2rem;
    font-size: 1.125rem;
}

.btn-sm {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
}

/* ============================================
   FORMS
   ============================================ */

.form-group {
    margin-bottom: var(--spacing-lg);
}

.form-label {
    display: block;
    margin-bottom: var(--spacing-sm);
    font-weight: 600;
    color: var(--text-primary);
}

.form-input,
.form-textarea,
.form-select {
    width: 100%;
    padding: 0.75rem 1rem;
    font-size: 1rem;
    font-family: inherit;
    color: var(--text-primary);
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.form-input:focus,
.form-textarea:focus,
.form-select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.form-textarea {
    min-height: 120px;
    resize: vertical;
}

/* ============================================
   CARDS
   ============================================ */

.card {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-fast);
}

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

.card-title {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: var(--spacing-md);
}

.card-content {
    color: var(--text-secondary);
}

/* ============================================
   FLASH MESSAGES
   ============================================ */

.flash-message {
    position: fixed;
    top: 80px;
    right: var(--spacing-lg);
    max-width: 400px;
    padding: var(--spacing-md) var(--spacing-lg);
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    z-index: var(--z-modal);
    animation: slideInRight var(--transition-base);
}

@keyframes slideInRight {
    from {
        transform: translateX(400px);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}

.flash-message.fade-out {
    animation: fadeOut var(--transition-base);
}

@keyframes fadeOut {
    to {
        opacity: 0;
        transform: translateX(400px);
    }
}

.flash-success {
    border-left: 4px solid var(--success-color);
}

.flash-error {
    border-left: 4px solid var(--error-color);
}

.flash-warning {
    border-left: 4px solid var(--warning-color);
}

.flash-info {
    border-left: 4px solid var(--info-color);
}

.flash-close {
    position: absolute;
    top: var(--spacing-sm);
    right: var(--spacing-sm);
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-tertiary);
    line-height: 1;
}

/* ============================================
   FOOTER
   ============================================ */

.site-footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    margin-top: var(--spacing-3xl);
}

.footer-main {
    padding: var(--spacing-3xl) 0 var(--spacing-2xl);
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1fr;
    gap: var(--spacing-2xl);
}

@media (max-width: 768px) {
    .footer-grid {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }
}

.footer-logo img {
    height: 36px;
    margin-bottom: var(--spacing-md);
}

.footer-description {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-lg);
}

.footer-social {
    display: flex;
    gap: var(--spacing-md);
}

.social-link {
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--bg-tertiary);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

.social-link:hover {
    background: var(--primary-color);
    color: white;
    transform: translateY(-2px);
}

.footer-heading {
    font-size: 1.125rem;
    font-weight: 700;
    margin-bottom: var(--spacing-lg);
    color: var(--text-primary);
}

.footer-links {
    list-style: none;
}

.footer-links li {
    margin-bottom: var(--spacing-sm);
}

.footer-links a {
    color: var(--text-secondary);
    font-size: 0.9375rem;
    transition: color var(--transition-fast);
}

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

.footer-bottom {
    border-top: 1px solid var(--border-color);
    padding: var(--spacing-lg) 0;
}

.footer-bottom-inner {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

@media (max-width: 768px) {
    .footer-bottom-inner {
        flex-direction: column;
        text-align: center;
    }
}

.copyright,
.footer-credits {
    font-size: 0.875rem;
    color: var(--text-tertiary);
}

.heart {
    color: var(--error-color);
}

/* ============================================
   SCROLL TO TOP
   ============================================ */

.scroll-to-top {
    position: fixed;
    bottom: var(--spacing-xl);
    right: var(--spacing-xl);
    width: 48px;
    height: 48px;
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: var(--radius-full);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow-lg);
    opacity: 0;
    pointer-events: none;
    transition: all var(--transition-base);
    z-index: var(--z-fixed);
}

.scroll-to-top.visible {
    opacity: 1;
    pointer-events: all;
}

.scroll-to-top:hover {
    background: var(--primary-hover);
    transform: translateY(-4px);
}

/* ============================================
   ADSENSE PLACEHOLDERS
   ============================================ */

.ad-container {
    margin: var(--spacing-2xl) 0;
    text-align: center;
}

.ad-label {
    font-size: 0.75rem;
    color: var(--text-tertiary);
    text-transform: uppercase;
    margin-bottom: var(--spacing-sm);
}

.ad-placeholder {
    background: var(--bg-secondary);
    border: 1px dashed var(--border-color);
    border-radius: var(--radius-md);
}

/* ============================================
   UTILITY CLASSES
   ============================================ */

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

.mt-sm { margin-top: var(--spacing-sm); }
.mt-md { margin-top: var(--spacing-md); }
.mt-lg { margin-top: var(--spacing-lg); }
.mt-xl { margin-top: var(--spacing-xl); }

.mb-sm { margin-bottom: var(--spacing-sm); }
.mb-md { margin-bottom: var(--spacing-md); }
.mb-lg { margin-bottom: var(--spacing-lg); }
.mb-xl { margin-bottom: var(--spacing-xl); }

.pt-sm { padding-top: var(--spacing-sm); }
.pt-md { padding-top: var(--spacing-md); }
.pt-lg { padding-top: var(--spacing-lg); }
.pt-xl { padding-top: var(--spacing-xl); }

.pb-sm { padding-bottom: var(--spacing-sm); }
.pb-md { padding-bottom: var(--spacing-md); }
.pb-lg { padding-bottom: var(--spacing-lg); }
.pb-xl { padding-bottom: var(--spacing-xl); }

.hidden { display: none !important; }
.visible { display: block !important; }

@media (max-width: 768px) {
    .hidden-mobile { display: none !important; }
}

@media (min-width: 769px) {
    .hidden-desktop { display: none !important; }
}