/* --- Design Tokens --- */
:root {
    /* Colors */
    --color-bg-dark: hsl(220, 30%, 8%);      /* Deep Ocean */
    --color-bg-light: hsl(0, 0%, 98%);       /* Sand White */
    --color-primary: hsl(200, 100%, 45%);    /* Clear Water Blue */
    --color-accent: hsl(35, 100%, 55%);      /* Sunset Orange/Gold */
    --color-text-main: hsl(0, 0%, 90%);
    --color-text-dark: hsl(220, 20%, 20%);
    --color-surface: hsl(220, 20%, 15%);
    
    /* Typography */
    --font-heading: 'Oswald', sans-serif;
    --font-body: 'Montserrat', sans-serif;
    
    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-smooth: 0.4s cubic-bezier(0.25, 0.8, 0.25, 1);
}

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

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

body {
    font-family: var(--font-body);
    background-color: var(--color-bg-dark);
    color: var(--color-text-main);
    line-height: 1.6;
    overflow-x: hidden;
}

a {
    text-decoration: none;
    color: inherit;
}

ul {
    list-style: none;
}

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

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 5%;
}

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

/* --- Typography System --- */
h1, h2, h3, h4 {
    font-family: var(--font-heading);
    text-transform: uppercase;
    line-height: 1.2;
}

.section-subtitle {
    color: var(--color-accent);
    font-family: var(--font-body);
    font-weight: 600;
    letter-spacing: 2px;
    font-size: 0.9rem;
    margin-bottom: 0.5rem;
    display: block;
}

.section-title {
    font-size: 2.5rem;
    margin-bottom: 2rem;
}

/* --- Header / Nav --- */
header {
    position: fixed;
    top: 0;
    width: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem 5%;
    z-index: 100;
    transition: var(--transition-smooth);
    background: transparent;
}

header.scrolled {
    background: rgba(15, 20, 30, 0.95);
    backdrop-filter: blur(10px);
    padding: 1rem 5%;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.5);
}

.logo {
    display: flex;
    align-items: center;
    font-size: 2rem;
    font-weight: 800;
    font-family: var(--font-heading);
    letter-spacing: 1px;
}
.water-drop-letter {
    height: 0.85em; /* Vừa vặn với font Oswald */
    width: auto;
    margin: 0 0.05em;
    position: relative;
    top: 0.08em; 
    color: var(--color-primary);
}
.logo-text {
    color: var(--color-primary);
}
.logo-accent {
    color: var(--color-accent);
}

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

nav a {
    font-size: 0.9rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 1px;
    position: relative;
    transition: var(--transition-fast);
}

nav ul li a:not(.nav-btn)::after {
    content: '';
    position: absolute;
    bottom: -5px;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--color-accent);
    transition: var(--transition-smooth);
}

nav ul li a:not(.nav-btn):hover::after {
    width: 100%;
}

.mobile-menu-btn {
    display: none;
    font-size: 1.5rem;
    cursor: pointer;
}

/* --- Buttons --- */
.btn-primary, .btn-secondary, .btn-outline {
    display: inline-block;
    padding: 12px 28px;
    font-family: var(--font-heading);
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 1px;
    border-radius: 4px;
    transition: var(--transition-smooth);
    cursor: pointer;
}

.btn-primary {
    background: var(--color-accent);
    color: var(--color-bg-dark);
    border: 2px solid var(--color-accent);
}

.btn-primary:hover {
    background: transparent;
    color: var(--color-accent);
}

.btn-secondary {
    background: rgba(255, 255, 255, 0.1);
    color: #fff;
    border: 1px solid rgba(255, 255, 255, 0.3);
    backdrop-filter: blur(5px);
}

.btn-secondary:hover {
    background: rgba(255, 255, 255, 0.2);
}

.btn-outline {
    background: transparent;
    border: 1px solid rgba(255, 255, 255, 0.2);
    color: #fff;
    padding: 10px 20px;
    font-size: 0.85rem;
}

.btn-outline:hover {
    border-color: var(--color-accent);
    color: var(--color-accent);
}

.large-btn {
    padding: 16px 40px;
    font-size: 1.1rem;
}

/* --- Hero Section --- */
.hero {
    position: relative;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
}

.hero-video {
    position: absolute;
    top: 50%;
    left: 50%;
    min-width: 100%;
    min-height: 100%;
    width: auto;
    height: auto;
    transform: translateX(-50%) translateY(-50%);
    object-fit: cover;
    z-index: -2;
}

.hero-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(to right, rgba(15, 20, 30, 0.8), rgba(15, 20, 30, 0.4));
    z-index: -1;
}

.hero-content {
    text-align: center;
    max-width: 800px;
    padding: 0 20px;
}

.sub-headline {
    color: var(--color-accent);
    font-family: var(--font-body);
    font-weight: 600;
    letter-spacing: 3px;
    font-size: 1.2rem;
    margin-bottom: 1rem;
}

.main-headline {
    font-size: 4.5rem;
    font-weight: 800;
    margin-bottom: 1.5rem;
    text-shadow: 0 4px 20px rgba(0,0,0,0.5);
}

.hero-description {
    font-size: 1.2rem;
    margin-bottom: 2.5rem;
    opacity: 0.9;
    font-weight: 300;
}

.hero-actions {
    display: flex;
    gap: 1.5rem;
    justify-content: center;
}

.play-icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 24px;
    height: 24px;
    background: #fff;
    color: var(--color-bg-dark);
    border-radius: 50%;
    font-size: 0.7rem;
    margin-right: 8px;
    padding-left: 2px;
}

/* --- Methodology Section --- */
.methodology {
    padding: 100px 0;
    background-color: var(--color-bg-light);
    color: var(--color-text-dark);
}

.flex-row {
    display: flex;
    align-items: center;
    gap: 60px;
}

.methodology-text {
    flex: 1;
}

.methodology-text .section-title {
    color: var(--color-bg-dark);
}

.methodology-text p {
    margin-bottom: 1.5rem;
    font-size: 1.05rem;
    color: #444;
}

.link-arrow {
    display: inline-block;
    margin-top: 10px;
    font-weight: 600;
    color: var(--color-primary);
    text-transform: uppercase;
    letter-spacing: 1px;
    font-size: 0.9rem;
    transition: var(--transition-fast);
}

.link-arrow:hover {
    color: var(--color-bg-dark);
    transform: translateX(5px);
}

.methodology-image {
    flex: 1;
}

.image-wrapper {
    position: relative;
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 20px 40px rgba(0,0,0,0.1);
}

.image-wrapper img {
    transition: transform 0.7s ease;
}

.image-wrapper:hover img {
    transform: scale(1.05);
}

.experience-badge {
    position: absolute;
    bottom: -20px;
    left: -20px;
    background: var(--color-accent);
    color: var(--color-bg-dark);
    padding: 30px;
    border-radius: 50%;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    width: 140px;
    height: 140px;
    text-align: center;
    font-family: var(--font-heading);
    box-shadow: 0 10px 20px rgba(0,0,0,0.2);
}

.experience-badge .years {
    font-size: 2.5rem;
    font-weight: 800;
    line-height: 1;
}

.experience-badge .text {
    font-size: 0.8rem;
    text-transform: uppercase;
}

/* --- Courses Section --- */
.courses {
    padding: 100px 0;
    background: url('https://images.unsplash.com/photo-1518182170546-076616fd4676?ixlib=rb-4.0.3&auto=format&fit=crop&w=1920&q=80') center/cover fixed;
    position: relative;
}

.courses::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(15, 20, 30, 0.9);
}

.courses .container {
    position: relative;
    z-index: 2;
}

.cards-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
    margin-top: 50px;
}

.course-card {
    background: var(--color-surface);
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 10px 30px rgba(0,0,0,0.3);
    border: 1px solid rgba(255,255,255,0.05);
    transition: var(--transition-smooth);
}

.course-card:hover {
    transform: translateY(-10px);
    box-shadow: 0 20px 40px rgba(0,0,0,0.5);
    border-color: rgba(255,255,255,0.1);
}

.card-image {
    height: 220px;
    background-size: cover;
    background-position: center;
    position: relative;
}

.card-tag {
    position: absolute;
    top: 15px;
    right: 15px;
    background: var(--color-accent);
    color: var(--color-bg-dark);
    font-size: 0.75rem;
    font-weight: 700;
    padding: 4px 12px;
    border-radius: 20px;
    text-transform: uppercase;
    font-family: var(--font-heading);
}

.card-content {
    padding: 25px;
    text-align: left;
}

.card-content h4 {
    font-size: 1.5rem;
    margin-bottom: 10px;
}

.card-content p {
    font-size: 0.9rem;
    color: #ccc;
    margin-bottom: 20px;
    line-height: 1.5;
}

.card-meta {
    display: flex;
    justify-content: space-between;
    font-size: 0.85rem;
    color: var(--color-primary);
    margin-bottom: 15px;
}
.location {
    color: var(--color-accent);
}
.card-price {
    font-size: 1.3rem;
    font-weight: 700;
    color: #fff;
    margin-bottom: 20px;
    padding-bottom: 15px;
    border-bottom: 1px solid rgba(255,255,255,0.1);
    font-family: var(--font-heading);
}

/* --- Locations Map Section --- */
.locations {
    padding: 100px 0;
    background-color: #0c1017;
}

.leaflet-popup-content-wrapper, .leaflet-popup-tip {
    background: var(--color-surface);
    color: #fff;
    border: 1px solid rgba(255,255,255,0.1);
}
.leaflet-popup-content h4 {
    font-family: var(--font-heading);
    color: var(--color-accent);
    font-size: 1.2rem;
    margin-bottom: 5px;
    letter-spacing: 1px;
}
.leaflet-popup-content p {
    font-family: var(--font-body);
    font-size: 0.9rem;
    color: #ccc;
    margin: 0;
}
.leaflet-container a {
    color: var(--color-primary);
}

/* --- CTA Banner --- */
.cta-banner {
    padding: 80px 0;
    background: linear-gradient(135deg, var(--color-bg-dark), var(--color-primary));
}

.cta-banner h2 {
    font-size: 2.5rem;
    margin-bottom: 15px;
}

.cta-banner p {
    font-size: 1.1rem;
    margin-bottom: 30px;
}

.cta-form {
    display: flex;
    justify-content: center;
    max-width: 600px;
    margin: 0 auto;
    gap: 10px;
}

.cta-form input {
    flex: 1;
    padding: 15px 20px;
    border: none;
    border-radius: 4px;
    font-family: var(--font-body);
    font-size: 1rem;
}

/* --- Footer --- */
footer {
    background: #080b11;
    padding: 60px 0 20px;
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr;
    gap: 40px;
    margin-bottom: 40px;
}

.footer-brand p {
    margin-top: 15px;
    color: #888;
    max-width: 300px;
}

.footer-links h4, .footer-contact h4 {
    font-family: var(--font-heading);
    color: #fff;
    margin-bottom: 20px;
    font-size: 1.2rem;
}

.footer-links ul li {
    margin-bottom: 10px;
}

.footer-links ul li a {
    color: #888;
    transition: var(--transition-fast);
}

.footer-links ul li a:hover {
    color: var(--color-accent);
}

.footer-contact p {
    color: #888;
    margin-bottom: 10px;
}

.footer-bottom {
    text-align: center;
    padding-top: 20px;
    border-top: 1px solid rgba(255,255,255,0.1);
    color: #555;
    font-size: 0.9rem;
}

/* --- Animations & Utilities --- */
.fade-in-up {
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.8s ease, transform 0.8s ease;
}

.slide-in-left {
    opacity: 0;
    transform: translateX(-40px);
    transition: 0.8s ease;
}

.slide-in-right {
    opacity: 0;
    transform: translateX(40px);
    transition: 0.8s ease;
}

.is-visible {
    opacity: 1;
    transform: translate(0);
}

/* --- Responsive --- */
@media screen and (max-width: 900px) {
    .flex-row {
        flex-direction: column;
    }
    
    .footer-grid {
        grid-template-columns: 1fr;
    }
    
    .main-headline {
        font-size: 3rem;
    }
}

@media screen and (max-width: 768px) {
    nav ul {
        display: none; /* simple hidden for mobile, in real would use menu */
    }
    
    .mobile-menu-btn {
        display: block;
    }
    
    .cta-form {
        flex-direction: column;
    }
}