:root {
    --primary-color: #3498db; 
    --light-blue-bg: #f0f8ff; 
    --white-color: #ffffff;
    --dark-text: #333333;
    --light-text: #555555;
    --shadow: 0 4px 15px rgba(0, 0, 0, 0.08);
    --shadow-hover: 0 8px 25px rgba(0, 0, 0, 0.15);
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Poppins', sans-serif;
    line-height: 1.6;
    color: var(--dark-text);
    background-color: var(--white-color);
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 2rem;
}

.section-padding {
    padding: 6rem 0;
}

.section-title {
    text-align: center;
    font-size: 2.5rem;
    margin-bottom: 4rem;
    font-weight: 600;
    color: var(--primary-color);
}

.btn {
    display: inline-block;
    padding: 12px 25px;
    background-color: var(--primary-color);
    color: var(--white-color);
    text-decoration: none;
    border-radius: 5px;
    font-weight: 600;
    box-shadow: 0 4px 10px rgba(52, 152, 219, 0.3);
    transition: all 0.3s ease;
}

.btn:hover {
    background-color: #2980b9;
    transform: translateY(-3px);
    box-shadow: 0 6px 15px rgba(52, 152, 219, 0.5);
}

#main-header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
    background: transparent;
    padding: 1rem 0;
    transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

#main-header.scrolled {
    background-color: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(10px);
    box-shadow: var(--shadow);
}

#main-header nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

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

.nav-links {
    display: flex;
    list-style: none;
}

.nav-links li {
    margin-left: 2rem;
}

.nav-links a {
    text-decoration: none;
    color: var(--dark-text);
    font-weight: 600;
    transition: color 0.3s ease;
}

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

#hero {
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    color: var(--dark-text);
    text-align: center;
    background: linear-gradient(135deg, var(--light-blue-bg) 0%, var(--white-color) 100%);
}

.hero-content {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 3rem;
}

.profile-pic-container {
    flex-shrink: 0;
}

.profile-pic {
    width: 200px;
    height: 200px;
    border-radius: 50%;
    object-fit: cover;
    border: 6px solid rgba(255, 255, 255, 0.8);
    box-shadow: var(--shadow-hover);
}

.hero-text {
    text-align: left;
    max-width: 600px;
}

.hero-text h1 {
    font-size: 3rem;
    margin-bottom: 1rem;
    font-weight: 700;
}

.hero-text p {
    font-size: 1.2rem;
    color: var(--light-text);
    margin-bottom: 2rem;
}

#skills {
    background-color: var(--light-blue-bg);
}

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

.skill-card {
    background: var(--white-color);
    padding: 2.5rem 2rem;
    border-radius: 10px;
    box-shadow: var(--shadow);
    text-align: center;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.skill-card:hover {
    transform: translateY(-10px);
    box-shadow: var(--shadow-hover);
}

.skill-logo {
    height: 50px;
    margin-bottom: 1.5rem;
}

.skill-card h3 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.5rem;
}

.projects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 2.5rem;
}

.project-card {
    background: var(--white-color);
    border-radius: 10px;
    overflow: hidden;
    box-shadow: var(--shadow);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    display: flex;
    flex-direction: column;
}

.project-card:hover {
    transform: translateY(-10px);
    box-shadow: var(--shadow-hover);
}

.project-image-container {
    position: relative;
    cursor: pointer;
}

.project-card img {
    width: 100%;
    height: 220px;
    object-fit: cover;
    display: block;
}

.overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(52, 152, 219, 0.7);
    opacity: 0;
    transition: opacity 0.4s ease;
    display: flex;
    justify-content: center;
    align-items: center;
}

.project-card:hover .overlay {
    opacity: 1;
}

.overlay::after {
    content: '자세히 보기';
    color: var(--white-color);
    font-size: 1.2rem;
    font-weight: 600;
    border: 2px solid var(--white-color);
    padding: 10px 20px;
    border-radius: 5px;
}

.project-info {
    padding: 1.5rem;
    flex-grow: 1;
    display: flex;
    flex-direction: column;
}

.project-info h3 {
    margin-bottom: 0.5rem;
}

.project-info p {
    margin-bottom: 1rem;
    color: var(--light-text);
    flex-grow: 1;
}

.project-link {
    text-decoration: none;
    color: var(--primary-color);
    font-weight: 600;
    align-self: flex-start;
}

#main-footer {
    background-color: #2c3e50;
    color: var(--white-color);
    text-align: center;
    padding: 2rem 0;
}

.fade-in {
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.6s ease-out, transform 0.6s ease-out;
}

.fade-in.visible {
    opacity: 1;
    transform: translateY(0);
}

@media (max-width: 768px) {
    .nav-links {
        display: none;
    }

    .section-title {
        font-size: 2rem;
    }
    
    .hero-content {
        flex-direction: column;
        text-align: center;
        padding-top: 5rem;
    }

    #hero {
        padding: 6rem 0;
    }
    
    .hero-text {
        text-align: center;
    }

    .hero-text h1 {
        font-size: 2.5rem;
    }
}