/* Global Styles */
:root {
    --primary-color: #2d5a3d;
    --secondary-color: #6fad8c;
    --accent-color: #8bc34a;
    --text-dark: #2c3e50;
    --text-light: #7f8c8d;
    --bg-light: #f0f7f4;
    --bg-white: #ffffff;
    --border-light: #e8f5e9;
    --shadow-sm: 0 2px 10px rgba(0,0,0,0.08);
    --shadow-md: 0 5px 20px rgba(0,0,0,0.1);
    --shadow-lg: 0 10px 40px rgba(0,0,0,0.15);
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', 'Noto Sans KR', sans-serif;
    color: var(--text-dark);
    line-height: 1.6;
    background-color: var(--bg-white);
    overflow-x: hidden;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: 400;
    line-height: 1.2;
    margin-bottom: 1rem;
}

h1, h2 {
    font-weight: 500;
}

h1 { font-size: clamp(2rem, 5vw, 3.5rem); }
h2 { font-size: clamp(1.5rem, 4vw, 2.5rem); }
h3 { font-size: clamp(1.2rem, 3vw, 1.8rem); }
h4 { font-size: clamp(1rem, 2vw, 1.3rem); }

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

/* Navigation */
.navbar {
    position: fixed;
    top: 0;
    width: 100%;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    box-shadow: 0 2px 20px rgba(0,0,0,0.05);
    z-index: 1000;
    transition: var(--transition);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.2rem 20px;
}

.nav-logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
    text-decoration: none;
    transition: var(--transition);
}

.nav-logo:hover {
    color: var(--secondary-color);
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 2rem;
}

.nav-link {
    color: var(--text-dark);
    text-decoration: none;
    font-weight: 500;
    position: relative;
    transition: var(--transition);
    padding: 0.5rem 0;
}

.nav-link::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--secondary-color);
    transition: width 0.3s ease;
}

.nav-link:hover::after {
    width: 100%;
}

.hamburger {
    display: none;
    flex-direction: column;
    cursor: pointer;
    gap: 4px;
}

.hamburger span {
    width: 25px;
    height: 2px;
    background: var(--text-dark);
    transition: var(--transition);
}

/* Hero Section */
.hero {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background: linear-gradient(135deg, #4caf50 0%, #81c784 50%, #a5d6a7 100%);
    background-size: 200% 200%;
    animation: gradientShift 15s ease infinite;
    color: white;
    position: relative;
    padding: 80px 20px;
}

@keyframes gradientShift {
    0% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
    100% { background-position: 0% 50%; }
}

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

.hero-title {
    color: white;
    margin-bottom: 1.5rem;
    font-weight: 700;
}

.highlight {
    background: linear-gradient(90deg, #fff, #c8e6c9);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: 1.2rem;
    margin-bottom: 2rem;
    opacity: 0.9;
    color: rgba(255, 255, 255, 0.9);
}

.hero-buttons {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
}

.btn {
    padding: 12px 30px;
    border-radius: 50px;
    font-weight: 500;
    text-decoration: none;
    transition: var(--transition);
    display: inline-block;
    border: 2px solid transparent;
}

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

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 30px rgba(0,0,0,0.2);
}

.btn-outline {
    background: transparent;
    color: white;
    border-color: white;
}

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

/* Scroll Indicator */
.scroll-indicator {
    position: absolute;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%);
    animation: bounce 2s infinite;
}

.scroll-indicator span {
    display: block;
    width: 30px;
    height: 50px;
    border: 2px solid white;
    border-radius: 25px;
    position: relative;
}

.scroll-indicator span::after {
    content: '';
    position: absolute;
    top: 10px;
    left: 50%;
    transform: translateX(-50%);
    width: 4px;
    height: 10px;
    background: white;
    border-radius: 2px;
    animation: scroll 2s infinite;
}

@keyframes bounce {
    0%, 20%, 50%, 80%, 100% { transform: translateX(-50%) translateY(0); }
    40% { transform: translateX(-50%) translateY(-10px); }
    60% { transform: translateX(-50%) translateY(-5px); }
}

@keyframes scroll {
    0% { opacity: 1; top: 10px; }
    100% { opacity: 0; top: 25px; }
}

/* About Section */
.about {
    padding: 100px 0;
    background: var(--bg-white);
}

.section-title {
    text-align: center;
    margin-bottom: 3rem;
    position: relative;
    color: var(--text-dark);
}

.section-title::after {
    content: '';
    position: absolute;
    bottom: -15px;
    left: 50%;
    transform: translateX(-50%);
    width: 60px;
    height: 3px;
    background: var(--secondary-color);
}

.about-content {
    display: grid;
    gap: 3rem;
}

.about-text h3 {
    margin-bottom: 1.5rem;
    color: var(--primary-color);
}

.education-info, .certification-info {
    margin: 2rem 0;
    padding: 1.5rem;
    background: var(--bg-light);
    border-radius: 10px;
}

.education-info h4, .certification-info h4 {
    color: var(--secondary-color);
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.education-info ul, .certification-info ul {
    list-style: none;
    padding: 0;
}

.education-info li, .certification-info li {
    padding: 0.5rem 0;
    padding-left: 1.5rem;
    position: relative;
    line-height: 1.8;
}

.education-info li::before, .certification-info li::before {
    content: '▪';
    position: absolute;
    left: 0;
    color: var(--secondary-color);
}

.skills {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-top: 3rem;
}

.skill-item {
    background: var(--bg-light);
    padding: 2rem;
    border-radius: 15px;
    text-align: center;
    transition: var(--transition);
}

.skill-item:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.skill-item i {
    font-size: 3rem;
    color: var(--secondary-color);
    margin-bottom: 1rem;
}

.skill-item h4 {
    margin-bottom: 0.5rem;
}

/* Career Section */
.career {
    padding: 100px 0;
    background: var(--bg-light);
}

.career-period {
    margin-bottom: 4rem;
}

.period-title {
    text-align: center;
    margin-bottom: 3rem;
    color: var(--text-dark);
    font-weight: 400;
    font-size: 1.3rem;
}

.timeline {
    position: relative;
    padding: 0 20px;
}

.timeline::before {
    content: '';
    position: absolute;
    top: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 2px;
    height: 100%;
    background: var(--border-light);
    z-index: -1;
}

.timeline-item {
    display: flex;
    margin-bottom: 3rem;
    position: relative;
    align-items: center;
}

.timeline-item:nth-child(odd) {
    flex-direction: row-reverse;
}

.timeline-year {
    flex: 0 0 100px;
    text-align: center;
    font-weight: 500;
    font-size: 1.1rem;
    color: var(--primary-color);
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--bg-light);
    padding: 0.5rem 1rem;
    border-radius: 20px;
    border: 2px solid var(--secondary-color);
    margin: 0 10px;
}

.timeline-year::after {
    content: '';
    position: absolute;
    width: 2px;
    height: 30px;
    background: var(--border-light);
    top: 100%;
    left: 50%;
    transform: translateX(-50%);
}

.timeline-content {
    flex: 1;
    background: white;
    padding: 1.5rem;
    border-radius: 10px;
    box-shadow: var(--shadow-sm);
    margin: 0 20px;
    transition: var(--transition);
    max-width: 500px;
}

.timeline-content:hover {
    box-shadow: var(--shadow-md);
    transform: scale(1.02);
}

.timeline-content h4 {
    color: var(--text-dark);
    margin-bottom: 0.5rem;
    font-weight: 400;
    font-size: 1rem;
}

.timeline-content p {
    margin-bottom: 0.5rem;
    font-size: 0.95rem;
    color: var(--text-dark);
    font-weight: 400;
}

/* Research Section */
.research {
    padding: 100px 0;
    background: var(--bg-white);
}

.research-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
    gap: 3rem;
}

.research-item {
    background: var(--bg-light);
    padding: 2.5rem;
    border-radius: 15px;
    transition: var(--transition);
}

.research-item:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.research-item i {
    font-size: 2.5rem;
    color: var(--secondary-color);
    margin-bottom: 1.5rem;
}

.research-item h3 {
    margin-bottom: 1.5rem;
    font-weight: 500;
}

.research-item ul {
    list-style: none;
}

.research-item li {
    padding: 0.5rem 0;
    padding-left: 1.5rem;
    position: relative;
    color: var(--text-light);
    line-height: 1.8;
}

.research-item li::before {
    content: '▪';
    position: absolute;
    left: 0;
    color: var(--secondary-color);
}

/* Contact Section */
.contact {
    padding: 100px 0;
    background: linear-gradient(135deg, #4caf50 0%, #81c784 50%, #a5d6a7 100%);
    color: white;
}

.contact .section-title {
    color: white;
}

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

.contact-content p {
    font-size: 1.2rem;
    margin-bottom: 2rem;
    color: rgba(255, 255, 255, 0.9);
}

.contact-info {
    display: flex;
    justify-content: center;
    gap: 2rem;
    flex-wrap: wrap;
}

.contact-item {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: white;
    text-decoration: none;
    padding: 1rem 1.5rem;
    border: 2px solid rgba(255, 255, 255, 0.3);
    border-radius: 50px;
    transition: var(--transition);
}

.contact-item:hover {
    background: rgba(255, 255, 255, 0.1);
    border-color: white;
    transform: translateY(-2px);
}

/* Footer */
.footer {
    padding: 2rem 0;
    background: var(--primary-color);
    color: white;
    text-align: center;
}

/* Animations */
.fade-in-up {
    opacity: 0;
    transform: translateY(30px);
    animation: fadeInUp 0.8s ease forwards;
}

.delay-1 { animation-delay: 0.2s; }
.delay-2 { animation-delay: 0.4s; }
.delay-3 { animation-delay: 0.6s; }

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

/* Responsive Design */
@media (max-width: 768px) {
    .nav-menu {
        position: fixed;
        left: -100%;
        top: 70px;
        flex-direction: column;
        background: white;
        width: 100%;
        text-align: center;
        transition: 0.3s;
        box-shadow: var(--shadow-md);
        padding: 2rem 0;
    }

    .nav-menu.active {
        left: 0;
    }

    .hamburger {
        display: flex;
    }

    .hero-buttons {
        flex-direction: column;
        align-items: center;
    }

    .timeline::before {
        left: 30px;
    }

    .timeline-item {
        flex-direction: column !important;
        padding-left: 60px;
    }

    .timeline-year {
        margin-bottom: 1rem;
        align-self: flex-start;
    }

    .timeline-year::after {
        display: none;
    }

    .timeline-content {
        margin: 0;
        max-width: 100%;
    }

    .skills {
        grid-template-columns: 1fr;
    }

    .research-content {
        grid-template-columns: 1fr;
    }

    .contact-info {
        flex-direction: column;
        align-items: center;
    }
}

@media (max-width: 480px) {
    .section-title {
        font-size: 1.8rem;
    }

    .hero-title {
        font-size: 2rem;
    }

    .hero-subtitle {
        font-size: 1rem;
    }

    .timeline-item {
        padding-left: 40px;
    }

    .timeline-year {
        font-size: 1rem;
        padding: 0.4rem 0.8rem;
    }
}