/* ===================================
   AI Study Buddy - Main Stylesheet
   =================================== */

/* CSS Reset & Variables */
:root {
    --primary-color: #4F46E5;
    --primary-dark: #4338CA;
    --primary-light: #818CF8;
    --secondary-color: #10B981;
    --accent-color: #F59E0B;
    --danger-color: #EF4444;
    --text-dark: #1F2937;
    --text-gray: #6B7280;
    --text-light: #9CA3AF;
    --bg-light: #F9FAFB;
    --bg-white: #FFFFFF;
    --border-color: #E5E7EB;
    --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);
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    color: var(--text-dark);
    background-color: var(--bg-light);
    line-height: 1.6;
    overflow-x: hidden;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 1rem;
    color: var(--text-dark);
}

h1 { font-size: 3rem; }
h2 { font-size: 2.25rem; }
h3 { font-size: 1.875rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.25rem; }
h6 { font-size: 1rem; }

p {
    margin-bottom: 1rem;
    color: var(--text-gray);
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.3s ease;
}

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

/* Container & Layout */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

.container-fluid {
    width: 100%;
    padding: 0 1.5rem;
}

.section {
    padding: 4rem 0;
}

/* Navigation */
.navbar {
    background-color: var(--bg-white);
    box-shadow: var(--shadow-sm);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 1000;
}

.navbar-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.logo-icon {
    font-size: 2rem;
}

.nav-links {
    display: flex;
    gap: 2rem;
    align-items: center;
}

.nav-link {
    color: var(--text-gray);
    font-weight: 500;
    transition: color 0.3s ease;
}

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

.nav-buttons {
    display: flex;
    gap: 1rem;
}

/* Buttons */
.btn {
    padding: 0.625rem 1.25rem;
    border-radius: var(--radius-md);
    font-weight: 600;
    font-size: 0.875rem;
    cursor: pointer;
    transition: all 0.3s ease;
    border: none;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    text-decoration: none;
}

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

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

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

.btn-secondary:hover {
    background-color: #059669;
    transform: translateY(-2px);
}

.btn-outline {
    background-color: transparent;
    border: 2px solid var(--primary-color);
    color: var(--primary-color);
}

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

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

.btn-danger:hover {
    background-color: #DC2626;
}

.btn-ghost {
    background-color: transparent;
    color: var(--text-gray);
}

.btn-ghost:hover {
    background-color: var(--bg-light);
    color: var(--text-dark);
}

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

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

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Cards */
.card {
    background-color: var(--bg-white);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    padding: 1.5rem;
    transition: all 0.3s ease;
}

.card:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-4px);
}

.card-header {
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 1rem;
    margin-bottom: 1rem;
}

.card-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.card-body {
    padding: 1rem 0;
}

.card-footer {
    border-top: 1px solid var(--border-color);
    padding-top: 1rem;
    margin-top: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

/* Forms */
.form-group {
    margin-bottom: 1.5rem;
}

.form-label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: var(--text-dark);
}

.form-input,
.form-textarea,
.form-select {
    width: 100%;
    padding: 0.75rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: 1rem;
    transition: all 0.3s ease;
    background-color: var(--bg-white);
}

.form-input:focus,
.form-textarea:focus,
.form-select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

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

.form-error {
    color: var(--danger-color);
    font-size: 0.875rem;
    margin-top: 0.25rem;
}

/* Grid System */
.grid {
    display: grid;
    gap: 2rem;
}

.grid-2 {
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}

.grid-3 {
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
}

.grid-4 {
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
}

/* Flex Utilities */
.flex {
    display: flex;
}

.flex-center {
    display: flex;
    justify-content: center;
    align-items: center;
}

.flex-between {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.flex-col {
    flex-direction: column;
}

.gap-1 { gap: 0.5rem; }
.gap-2 { gap: 1rem; }
.gap-3 { gap: 1.5rem; }
.gap-4 { gap: 2rem; }

/* Badges & Tags */
.badge {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    border-radius: 9999px;
    font-size: 0.75rem;
    font-weight: 600;
}

.badge-primary {
    background-color: #EEF2FF;
    color: var(--primary-color);
}

.badge-success {
    background-color: #D1FAE5;
    color: var(--secondary-color);
}

.badge-warning {
    background-color: #FEF3C7;
    color: var(--accent-color);
}

.badge-danger {
    background-color: #FEE2E2;
    color: var(--danger-color);
}

/* Loading Spinner */
.spinner {
    border: 3px solid var(--border-color);
    border-top: 3px solid var(--primary-color);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Alerts */
.alert {
    padding: 1rem 1.25rem;
    border-radius: var(--radius-md);
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.alert-info {
    background-color: #EEF2FF;
    color: var(--primary-color);
    border-left: 4px solid var(--primary-color);
}

.alert-success {
    background-color: #D1FAE5;
    color: var(--secondary-color);
    border-left: 4px solid var(--secondary-color);
}

.alert-warning {
    background-color: #FEF3C7;
    color: var(--accent-color);
    border-left: 4px solid var(--accent-color);
}

.alert-danger {
    background-color: #FEE2E2;
    color: var(--danger-color);
    border-left: 4px solid var(--danger-color);
}

/* Modal */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.5);
    display: none;
    justify-content: center;
    align-items: center;
    z-index: 2000;
    padding: 1rem;
}

.modal-overlay.active {
    display: flex;
}

.modal {
    background-color: var(--bg-white);
    border-radius: var(--radius-xl);
    max-width: 500px;
    width: 100%;
    max-height: 90vh;
    overflow-y: auto;
    box-shadow: var(--shadow-xl);
}

.modal-header {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.modal-title {
    font-size: 1.5rem;
    font-weight: 600;
    margin: 0;
}

.modal-close {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-gray);
    padding: 0;
    width: 2rem;
    height: 2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-sm);
    transition: all 0.3s ease;
}

.modal-close:hover {
    background-color: var(--bg-light);
    color: var(--text-dark);
}

.modal-body {
    padding: 1.5rem;
}

.modal-footer {
    padding: 1.5rem;
    border-top: 1px solid var(--border-color);
    display: flex;
    justify-content: flex-end;
    gap: 1rem;
}

/* Utilities */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mt-4 { margin-top: 2rem; }

.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }
.mb-4 { margin-bottom: 2rem; }

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

/* Responsive */
@media (max-width: 768px) {
    h1 { font-size: 2rem; }
    h2 { font-size: 1.75rem; }
    h3 { font-size: 1.5rem; }
    
    .container {
        padding: 0 1rem;
    }
    
    .section {
        padding: 2rem 0;
    }
    
    /* Enhanced Mobile Navigation */
    .navbar {
        padding: 0.75rem 0;
    }
    
    .nav-buttons {
        display: flex;
        flex-direction: column;
        width: 100%;
        gap: 0.5rem;
        padding: 1rem;
        background: var(--bg-white);
        border-top: 1px solid var(--border-color);
        margin-top: 0.5rem;
    }
    
    .nav-buttons .btn {
        width: 100%;
        text-align: center;
        justify-content: center;
    }
    
    .language-switcher {
        order: -1;
        margin-bottom: 0.5rem;
    }
    
    /* Mobile Menu Toggle */
    .nav-toggle {
        display: block;
        background: none;
        border: none;
        font-size: 1.5rem;
        cursor: pointer;
        padding: 0.5rem;
        color: var(--text-dark);
    }
    
    .nav-menu {
        position: fixed;
        top: 60px;
        left: -100%;
        width: 80%;
        max-width: 300px;
        height: calc(100vh - 60px);
        background: var(--bg-white);
        box-shadow: var(--shadow-xl);
        transition: left 0.3s ease;
        overflow-y: auto;
        z-index: 999;
    }
    
    .nav-menu.active {
        left: 0;
    }
    
    .nav-menu li {
        border-bottom: 1px solid var(--border-color);
    }
    
    .nav-menu a {
        display: block;
        padding: 1rem 1.5rem;
        font-size: 1.125rem;
    }
    
    /* Mobile Overlay */
    .mobile-overlay {
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: rgba(0, 0, 0, 0.5);
        opacity: 0;
        visibility: hidden;
        transition: opacity 0.3s ease, visibility 0.3s ease;
        z-index: 998;
    }
    
    .mobile-overlay.active {
        opacity: 1;
        visibility: visible;
    }
    
    .nav-links {
        display: none;
    }
    
    .grid {
        gap: 1rem;
    }
    
    .grid-3, .grid-2 {
        grid-template-columns: 1fr;
    }
    
    .card {
        padding: 1rem;
    }
    
    /* Mobile Stats Grid */
    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 1rem;
    }
    
    /* Mobile Buttons */
    .btn-lg {
        padding: 0.875rem 1.5rem;
        font-size: 1rem;
    }
    
    /* Mobile Modal */
    .modal {
        width: 95%;
        max-height: 90vh;
        overflow-y: auto;
    }
    
    /* Mobile Help Widget */
    .help-widget {
        flex-direction: column;
        text-align: center;
    }
    
    .help-widget > div:first-child {
        min-width: 100%;
    }
    
    /* Mobile Video Container */
    .video-container {
        border-radius: 8px;
    }
    
    /* Mobile Course Cards */
    .course-card {
        margin-bottom: 1rem;
    }
    
    /* Mobile Section Header */
    .section-header {
        flex-direction: column;
        gap: 1rem;
        align-items: stretch;
    }
    
    .section-header .btn {
        width: 100%;
    }
}

/* Small Mobile Devices */
@media (max-width: 480px) {
    h1 { font-size: 1.75rem; }
    h2 { font-size: 1.5rem; }
    
    .stats-grid {
        grid-template-columns: 1fr;
    }
    
    .btn {
        padding: 0.75rem 1rem;
        font-size: 0.875rem;
    }
    
    .navbar-content {
        flex-wrap: wrap;
    }
    
    .logo {
        font-size: 1.25rem;
    }
}