/**
 * KHÓA HỌC VIỆT - Design System
 * Light Theme Default - Tươi sáng, hiện đại
 * =====================================
 */

/* Google Fonts */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&family=Nunito:wght@600;700;800;900&display=swap');

/* CSS Variables - Light Theme Default */
:root {
    /* Colors - Bright & Fresh */
    --primary: #0ea5e9;
    --primary-dark: #0284c7;
    --primary-light: #7dd3fc;
    --secondary: #f97316;
    --secondary-dark: #ea580c;
    --secondary-light: #fdba74;

    --success: #22c55e;
    --warning: #eab308;
    --error: #ef4444;
    --info: #3b82f6;

    /* Light Theme */
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    --bg-card: #ffffff;
    --bg-card-hover: #f8fafc;

    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-muted: #94a3b8;

    --border-color: #e2e8f0;
    --border-light: #f1f5f9;

    /* Gradients */
    --gradient-primary: linear-gradient(135deg, #0ea5e9 0%, #06b6d4 100%);
    --gradient-secondary: linear-gradient(135deg, #f97316 0%, #fb923c 100%);
    --gradient-hero: linear-gradient(135deg, #0ea5e9 0%, #0284c7 50%, #0369a1 100%);
    --gradient-card: linear-gradient(180deg, rgba(14, 165, 233, 0.05) 0%, rgba(255, 255, 255, 0) 100%);

    /* Package Colors */
    --pkg-basic: #3b82f6;
    --pkg-intermediate: #8b5cf6;
    --pkg-ultimate: #f97316;

    /* Spacing */
    --space-xs: 0.25rem;
    --space-sm: 0.5rem;
    --space-md: 1rem;
    --space-lg: 1.5rem;
    --space-xl: 2rem;
    --space-2xl: 3rem;
    --space-3xl: 4rem;

    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-2xl: 1.5rem;
    --radius-full: 9999px;

    /* Shadows */
    --shadow-sm: 0 1px 2px 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);
    --shadow-card: 0 4px 20px rgba(0, 0, 0, 0.08);
    --shadow-card-hover: 0 12px 40px rgba(14, 165, 233, 0.15);

    /* Typography */
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-display: 'Nunito', var(--font-sans);

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 350ms ease;
}

/* Dark Theme */
[data-theme="dark"] {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --bg-card: #1e293b;
    --bg-card-hover: #334155;

    --text-primary: #f8fafc;
    --text-secondary: #cbd5e1;
    --text-muted: #64748b;

    --border-color: #334155;
    --border-light: #1e293b;

    --shadow-card: 0 4px 20px rgba(0, 0, 0, 0.3);
    --shadow-card-hover: 0 12px 40px rgba(14, 165, 233, 0.2);
}

/* Reset & Base */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-sans);
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

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

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

img {
    max-width: 100%;
    height: auto;
    display: block;
}

button {
    font: inherit;
    cursor: pointer;
    border: none;
    background: none;
}

input,
textarea,
select {
    font: inherit;
    color: inherit;
}

/* =====================================
   UTILITIES
   ===================================== */

/* Container */
.container {
    width: 100%;
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 var(--space-md);
}

@media (min-width: 640px) {
    .container {
        padding: 0 var(--space-lg);
    }
}

@media (min-width: 1024px) {
    .container {
        padding: 0 var(--space-xl);
    }
}

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

.grid-cols-1 {
    grid-template-columns: repeat(1, 1fr);
}

@media (min-width: 640px) {
    .sm\:grid-cols-2 {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 768px) {
    .md\:grid-cols-3 {
        grid-template-columns: repeat(3, 1fr);
    }

    .md\:grid-cols-4 {
        grid-template-columns: repeat(4, 1fr);
    }
}

@media (min-width: 1024px) {
    .lg\:grid-cols-4 {
        grid-template-columns: repeat(4, 1fr);
    }

    .lg\:grid-cols-5 {
        grid-template-columns: repeat(5, 1fr);
    }
}

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

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

.flex-wrap {
    flex-wrap: wrap;
}

.flex-1 {
    flex: 1;
}

.items-center {
    align-items: center;
}

.items-start {
    align-items: flex-start;
}

.items-end {
    align-items: flex-end;
}

.justify-center {
    justify-content: center;
}

.justify-between {
    justify-content: space-between;
}

.justify-end {
    justify-content: flex-end;
}

.gap-xs {
    gap: var(--space-xs);
}

.gap-sm {
    gap: var(--space-sm);
}

.gap-md {
    gap: var(--space-md);
}

.gap-lg {
    gap: var(--space-lg);
}

.gap-xl {
    gap: var(--space-xl);
}

/* Spacing */
.mt-sm {
    margin-top: var(--space-sm);
}

.mt-md {
    margin-top: var(--space-md);
}

.mt-lg {
    margin-top: var(--space-lg);
}

.mt-xl {
    margin-top: var(--space-xl);
}

.mt-2xl {
    margin-top: var(--space-2xl);
}

.mb-sm {
    margin-bottom: var(--space-sm);
}

.mb-md {
    margin-bottom: var(--space-md);
}

.mb-lg {
    margin-bottom: var(--space-lg);
}

.mb-xl {
    margin-bottom: var(--space-xl);
}

.mb-2xl {
    margin-bottom: var(--space-2xl);
}

.p-sm {
    padding: var(--space-sm);
}

.p-md {
    padding: var(--space-md);
}

.p-lg {
    padding: var(--space-lg);
}

.p-xl {
    padding: var(--space-xl);
}

.py-sm {
    padding-top: var(--space-sm);
    padding-bottom: var(--space-sm);
}

.py-md {
    padding-top: var(--space-md);
    padding-bottom: var(--space-md);
}

.py-lg {
    padding-top: var(--space-lg);
    padding-bottom: var(--space-lg);
}

.py-xl {
    padding-top: var(--space-xl);
    padding-bottom: var(--space-xl);
}

.py-2xl {
    padding-top: var(--space-2xl);
    padding-bottom: var(--space-2xl);
}

.py-3xl {
    padding-top: var(--space-3xl);
    padding-bottom: var(--space-3xl);
}

.px-sm {
    padding-left: var(--space-sm);
    padding-right: var(--space-sm);
}

.px-md {
    padding-left: var(--space-md);
    padding-right: var(--space-md);
}

.px-lg {
    padding-left: var(--space-lg);
    padding-right: var(--space-lg);
}

/* Text */
.text-center {
    text-align: center;
}

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

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

.text-xs {
    font-size: 0.75rem;
}

.text-sm {
    font-size: 0.875rem;
}

.text-base {
    font-size: 1rem;
}

.text-lg {
    font-size: 1.125rem;
}

.text-xl {
    font-size: 1.25rem;
}

.text-2xl {
    font-size: 1.5rem;
}

.text-3xl {
    font-size: 1.875rem;
}

.text-4xl {
    font-size: 2.25rem;
}

.text-5xl {
    font-size: 3rem;
}

.font-normal {
    font-weight: 400;
}

.font-medium {
    font-weight: 500;
}

.font-semibold {
    font-weight: 600;
}

.font-bold {
    font-weight: 700;
}

.font-extrabold {
    font-weight: 800;
}

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

.text-muted {
    color: var(--text-muted);
}

.text-primary-color {
    color: var(--primary);
}

.text-success {
    color: var(--success);
}

.text-warning {
    color: var(--warning);
}

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

.text-white {
    color: #ffffff;
}

/* Display */
.hidden {
    display: none !important;
}

.block {
    display: block;
}

.inline-block {
    display: inline-block;
}

.w-full {
    width: 100%;
}

.h-full {
    height: 100%;
}

.min-h-screen {
    min-height: 100vh;
}

.overflow-hidden {
    overflow: hidden;
}

.relative {
    position: relative;
}

.absolute {
    position: absolute;
}

.fixed {
    position: fixed;
}

.sticky {
    position: sticky;
}

.inset-0 {
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
}

.top-0 {
    top: 0;
}

.left-0 {
    left: 0;
}

.right-0 {
    right: 0;
}

/* Responsive hide/show */
@media (max-width: 767px) {
    .hide-mobile {
        display: none !important;
    }
}

@media (min-width: 768px) {
    .hide-desktop {
        display: none !important;
    }
}

/* =====================================
   COMPONENTS
   ===================================== */

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    padding: 0.75rem 1.5rem;
    font-weight: 600;
    font-size: 0.9375rem;
    border-radius: var(--radius-lg);
    transition: all var(--transition-base);
    cursor: pointer;
    white-space: nowrap;
    text-decoration: none;
    border: none;
}

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

.btn-primary {
    background: var(--gradient-primary);
    color: white;
    box-shadow: 0 4px 15px rgba(14, 165, 233, 0.3);
}

.btn-primary:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(14, 165, 233, 0.4);
    color: white;
}

.btn-secondary {
    background: var(--gradient-secondary);
    color: white;
    box-shadow: 0 4px 15px rgba(249, 115, 22, 0.3);
}

.btn-secondary:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(249, 115, 22, 0.4);
    color: white;
}

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

.btn-outline:hover:not(:disabled) {
    background: var(--primary);
    color: white;
}

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

.btn-white:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

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

.btn-ghost:hover:not(:disabled) {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

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

.btn-lg {
    padding: 1rem 2rem;
    font-size: 1.0625rem;
}

.btn-icon {
    width: 44px;
    height: 44px;
    padding: 0;
    border-radius: var(--radius-lg);
}

/* Cards */
.card {
    background: var(--bg-card);
    border-radius: var(--radius-xl);
    border: 1px solid var(--border-color);
    overflow: hidden;
    transition: all var(--transition-base);
    box-shadow: var(--shadow-card);
}

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

.card-body {
    padding: var(--space-lg);
}

.card-img {
    width: 100%;
    aspect-ratio: 16 / 9;
    object-fit: cover;
}

/* Form Elements */
.form-group {
    margin-bottom: var(--space-lg);
}

.form-label {
    display: block;
    margin-bottom: var(--space-sm);
    font-weight: 600;
    color: var(--text-primary);
    font-size: 0.875rem;
}

.form-input {
    width: 100%;
    padding: 0.875rem 1rem;
    background: var(--bg-secondary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    color: var(--text-primary);
    transition: all var(--transition-fast);
}

.form-input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 4px rgba(14, 165, 233, 0.1);
    background: var(--bg-primary);
}

.form-input::placeholder {
    color: var(--text-muted);
}

.form-select {
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 24 24' stroke='%2394a3b8'%3E%3Cpath stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='M19 9l-7 7-7-7'%3E%3C/path%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 1rem center;
    background-size: 1.25rem;
    padding-right: 3rem;
}

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

/* Badges */
.badge {
    display: inline-flex;
    align-items: center;
    padding: 0.25rem 0.75rem;
    font-size: 0.75rem;
    font-weight: 700;
    border-radius: var(--radius-full);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.badge-primary {
    background: rgba(14, 165, 233, 0.15);
    color: var(--primary);
}

.badge-secondary {
    background: rgba(249, 115, 22, 0.15);
    color: var(--secondary);
}

.badge-success {
    background: rgba(34, 197, 94, 0.15);
    color: var(--success);
}

.badge-warning {
    background: rgba(234, 179, 8, 0.15);
    color: var(--warning);
}

.badge-error {
    background: rgba(239, 68, 68, 0.15);
    color: var(--error);
}

/* Alert */
.alert {
    padding: var(--space-md) var(--space-lg);
    border-radius: var(--radius-lg);
    margin-bottom: var(--space-md);
    display: flex;
    align-items: flex-start;
    gap: var(--space-md);
}

.alert-success {
    background: rgba(34, 197, 94, 0.1);
    border: 1px solid var(--success);
    color: var(--success);
}

.alert-error {
    background: rgba(239, 68, 68, 0.1);
    border: 1px solid var(--error);
    color: var(--error);
}

.alert-warning {
    background: rgba(234, 179, 8, 0.1);
    border: 1px solid var(--warning);
    color: #92400e;
}

.alert-info {
    background: rgba(14, 165, 233, 0.1);
    border: 1px solid var(--primary);
    color: var(--primary-dark);
}

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

.header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
}

[data-theme="dark"] .header {
    background: rgba(15, 23, 42, 0.95);
}

.header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 72px;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-family: var(--font-display);
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary);
}

.logo-icon {
    width: 40px;
    height: 40px;
    background: var(--gradient-primary);
    border-radius: var(--radius-lg);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
}

.nav {
    display: none;
}

@media (min-width: 1024px) {
    .nav {
        display: flex;
        align-items: center;
        gap: var(--space-xl);
    }
}

/* Nav Link */
.nav-link {
    font-weight: 500;
    color: var(--text-secondary);
    transition: color var(--transition-fast);
    position: relative;
    padding: var(--space-sm) 0;
}

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

/* Highlighted Nav Item (Khóa 5+) */
.nav-link.nav-highlight {
    display: inline-flex;
    align-items: center;
    color: #ff7e5f;
    /* Orange */
    font-weight: 800;
    border: 2px solid #ff7e5f;
    background: rgba(255, 126, 95, 0.05);
    /* Very subtle bg */
    padding: 0.35rem 0.85rem;
    border-radius: 99px;
    /* Crown shape needs pill */
    margin-left: var(--space-xs);
    text-transform: uppercase;
    font-size: 0.85rem;
    box-shadow: 0 2px 10px rgba(255, 126, 95, 0.2);
    transition: all 0.3s ease;
}

.nav-link.nav-highlight:hover {
    background: #ff7e5f;
    color: white;
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(255, 126, 95, 0.3);
}

.nav-link.nav-highlight svg {
    margin-right: 6px !important;
    transition: transform 0.3s ease;
}

.nav-link.nav-highlight:hover svg {
    transform: scale(1.1) rotate(-10deg);
}

.nav-link.active::after {
    content: '';
    position: absolute;
    bottom: -4px;
    left: 0;
    width: 100%;
    height: 3px;
    background: var(--gradient-primary);
    border-radius: 2px;
}

.header-actions {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

/* Mobile Menu */
.mobile-menu-btn {
    display: flex;
    flex-direction: column;
    gap: 5px;
    padding: 10px;
    background: var(--bg-secondary);
    border-radius: var(--radius-md);
}

.mobile-menu-btn span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--text-primary);
    transition: all var(--transition-fast);
    border-radius: 1px;
}

@media (min-width: 1024px) {
    .mobile-menu-btn {
        display: none;
    }
}

.mobile-nav {
    position: fixed;
    top: 72px;
    left: 0;
    right: 0;
    bottom: 0;
    background: var(--bg-primary);
    padding: var(--space-lg);
    transform: translateX(-100%);
    transition: transform var(--transition-base);
    z-index: 99;
    overflow-y: auto;
}

.mobile-nav.active {
    transform: translateX(0);
}

.mobile-nav-link {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    padding: var(--space-md);
    font-size: 1.0625rem;
    font-weight: 600;
    color: var(--text-primary);
    border-radius: var(--radius-lg);
    transition: background var(--transition-fast);
}

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

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

.footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    padding: var(--space-3xl) 0 var(--space-xl);
    margin-top: auto;
}

.footer-grid {
    display: grid;
    gap: var(--space-xl);
    margin-bottom: var(--space-2xl);
}

@media (min-width: 640px) {
    .footer-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 768px) {
    .footer-grid {
        grid-template-columns: 2fr 1fr 1fr 1fr;
    }
}

.footer-brand {
    max-width: 280px;
}

.footer-title {
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: var(--space-md);
}

.footer-links {
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
}

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

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

.footer-bottom {
    padding-top: var(--space-xl);
    border-top: 1px solid var(--border-color);
    text-align: center;
    color: var(--text-muted);
    font-size: 0.875rem;
}

.social-links {
    display: flex;
    gap: var(--space-sm);
    margin-top: var(--space-md);
}

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

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

/* =====================================
   ANIMATIONS
   ===================================== */

@keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes float {

    0%,
    100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-10px);
    }
}

@keyframes pulse {

    0%,
    100% {
        transform: scale(1);
    }

    50% {
        transform: scale(1.05);
    }
}

.animate-fadeIn {
    animation: fadeIn var(--transition-base) ease-out;
}

.animate-fadeInUp {
    animation: fadeInUp 0.5s ease-out;
}

.animate-float {
    animation: float 3s ease-in-out infinite;
}

.animate-pulse {
    animation: pulse 2s ease-in-out infinite;
}

/* Skeleton Loading */
.skeleton {
    background: linear-gradient(90deg, var(--bg-secondary) 25%, var(--bg-tertiary) 50%, var(--bg-secondary) 75%);
    background-size: 200% 100%;
    animation: shimmer 1.5s infinite;
    border-radius: var(--radius-md);
}

@keyframes shimmer {
    0% {
        background-position: -200% 0;
    }

    100% {
        background-position: 200% 0;
    }
}

/* =====================================
   RESPONSIVE
   ===================================== */

@media (max-width: 639px) {
    html {
        font-size: 15px;
    }

    .text-4xl {
        font-size: 1.875rem;
    }

    .text-5xl {
        font-size: 2.25rem;
    }

    .btn {
        padding: 0.625rem 1.25rem;
    }

    .btn-lg {
        padding: 0.875rem 1.75rem;
    }
}