/* ===================================
   CSS Variables - Design System
   =================================== */
:root {
    /* Colors */
    --color-bg: #F9FAFB;
    --color-bg-secondary: #F3F4F6;
    --color-text-primary: #111827;
    --color-text-secondary: #6B7280;
    --color-text-tertiary: #9CA3AF;
    --color-accent: #3B82F6;
    --color-accent-hover: #2563EB;
    --color-white: #FFFFFF;
    --color-border: #E5E7EB;
    
    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-weight-normal: 400;
    --font-weight-medium: 500;
    --font-weight-semibold: 600;
    --font-weight-bold: 700;
    --font-weight-extrabold: 800;
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-2xl: 4rem;
    --spacing-3xl: 6rem;
    
    /* Border Radius */
    --radius-sm: 0.5rem;
    --radius-md: 0.75rem;
    --radius-lg: 1rem;
    --radius-full: 9999px;
    
    /* Shadows */
    --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);
    
    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 200ms ease;
    --transition-slow: 300ms ease;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-primary);
    font-size: 1rem;
    line-height: 1.6;
    color: var(--color-text-primary);
    background-color: var(--color-bg);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* ===================================
   Typography
   =================================== */
h1, h2, h3, h4, h5, h6 {
    font-weight: var(--font-weight-bold);
    line-height: 1.2;
    color: var(--color-text-primary);
}

h1 {
    font-size: 3.5rem;
    font-weight: var(--font-weight-extrabold);
}

h2 {
    font-size: 2.5rem;
}

h3 {
    font-size: 1.5rem;
}

p {
    color: var(--color-text-secondary);
    line-height: 1.7;
}

strong {
    font-weight: var(--font-weight-semibold);
    color: var(--color-text-primary);
}

/* ===================================
   Container
   =================================== */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

/* ===================================
   Sections
   =================================== */
.section {
    padding: var(--spacing-3xl) 0;
}

.section-gray {
    background-color: var(--color-bg-secondary);
}

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

.section-subtitle {
    text-align: center;
    color: var(--color-text-secondary);
    font-size: 1.125rem;
    margin-bottom: var(--spacing-xl);
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

/* ===================================
   Hero Section
   =================================== */
.hero {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: var(--spacing-2xl) 0;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(135deg, rgba(59, 130, 246, 0.9) 0%, rgba(99, 102, 241, 0.9) 100%);
    z-index: 1;
}

.hero-content {
    position: relative;
    z-index: 2;
    animation: fadeInUp 1s ease-out;
}

.hero-title {
    font-size: 4rem;
    font-weight: var(--font-weight-extrabold);
    color: var(--color-white);
    margin-bottom: var(--spacing-md);
    line-height: 1.1;
}

.flip-logo {
    display: inline-block;
    animation: float 3s ease-in-out infinite;
    font-size: 3.5rem;
    vertical-align: middle;
    margin-left: 0.5rem;
}

@keyframes float {
    0%, 100% { 
        transform: translateY(0); 
    }
    50% { 
        transform: translateY(-15px); 
    }
}

.hero-subtitle {
    font-size: 1.5rem;
    font-weight: var(--font-weight-medium);
    color: rgba(255, 255, 255, 0.95);
    margin-bottom: var(--spacing-xl);
}

.hero-cta {
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
    flex-wrap: wrap;
}

/* ===================================
   Buttons
   =================================== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 0 1.75rem;
    font-size: 1rem;
    font-weight: var(--font-weight-semibold);
    text-decoration: none;
    border-radius: 0.5rem;
    transition: transform 0.2s ease, box-shadow 0.2s ease, background-color 0.2s ease, color 0.2s ease;
    cursor: pointer;
    border: 2px solid transparent;
    white-space: nowrap;
    line-height: 1.5;
    height: 48px;
    min-height: 48px;
    max-height: 48px;
    box-sizing: border-box;
    flex-shrink: 0;
    overflow: hidden;
}

.btn svg {
    flex-shrink: 0;
    width: 20px;
    height: 20px;
}

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

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.15);
}

.btn-primary:active {
    transform: translateY(0);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

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

.btn-secondary:hover {
    background-color: var(--color-white);
    color: var(--color-accent);
    transform: translateY(-2px);
}

.btn-secondary:active {
    transform: translateY(0);
    background-color: rgba(255, 255, 255, 0.95);
}

/* ===================================
   About Section
   =================================== */
.about-content {
    max-width: 800px;
    margin: 0 auto;
}

.about-text {
    font-size: 1.25rem;
    line-height: 1.8;
    text-align: center;
    color: var(--color-text-secondary);
}

/* ===================================
   Projects Section
   =================================== */
.projects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-xl);
}

.project-card {
    background: var(--color-white);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-base);
    display: flex;
    flex-direction: column;
    height: 100%;
}

.project-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-xl);
}

.project-header {
    margin-bottom: var(--spacing-md);
}

.project-title {
    font-size: 1.25rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-sm);
    line-height: 1.3;
}

.project-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
    margin-top: var(--spacing-sm);
}

.tag {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    background-color: var(--color-bg-secondary);
    color: var(--color-text-secondary);
    font-size: 0.875rem;
    font-weight: var(--font-weight-medium);
    border-radius: var(--radius-full);
}

.project-description {
    color: var(--color-text-secondary);
    line-height: 1.7;
    margin-bottom: var(--spacing-md);
    flex-grow: 1;
}

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

.project-meta {
    display: flex;
    gap: var(--spacing-sm);
    align-items: center;
    font-size: 0.875rem;
    color: var(--color-text-tertiary);
}

.project-year {
    font-weight: var(--font-weight-medium);
}

.project-award,
.project-type {
    font-weight: var(--font-weight-semibold);
}

.project-link {
    display: inline-flex;
    align-items: center;
    gap: 0.375rem;
    color: var(--color-accent);
    font-weight: var(--font-weight-semibold);
    text-decoration: none;
    font-size: 0.875rem;
    transition: color var(--transition-fast);
}

.project-link:hover {
    color: var(--color-accent-hover);
}

.project-link svg {
    transition: transform var(--transition-fast);
}

.project-link:hover svg {
    transform: translateX(2px);
}

.project-images {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-sm);
    margin-top: var(--spacing-md);
    margin-bottom: var(--spacing-md);
}

.project-image {
    width: 100%;
    height: auto;
    border-radius: var(--radius-sm);
    object-fit: cover;
    transition: transform var(--transition-base);
    cursor: pointer;
}

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

@media (max-width: 768px) {
    .project-images {
        grid-template-columns: 1fr;
    }
}

/* ===================================
   Skills Section
   =================================== */
.skills-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-xl);
    margin-top: var(--spacing-xl);
}

@media (min-width: 1024px) {
    .skills-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 1400px) {
    .skills-grid {
        grid-template-columns: repeat(4, 1fr);
    }
}

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

.skill-category-title {
    font-size: 1.25rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-md);
}

.skills-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
    justify-content: center;
}

.skill-tag {
    display: inline-block;
    padding: 0.5rem 1rem;
    background-color: var(--color-white);
    color: var(--color-text-secondary);
    font-size: 0.875rem;
    font-weight: var(--font-weight-medium);
    border-radius: var(--radius-full);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-fast);
}

.skill-tag:hover {
    background-color: var(--color-accent);
    color: var(--color-white);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

/* ===================================
   Education Section
   =================================== */
.timeline {
    max-width: 800px;
    margin: var(--spacing-xl) auto 0;
    position: relative;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 20px;
    top: 0;
    bottom: 0;
    width: 2px;
    background-color: var(--color-accent);
}

.timeline-item {
    position: relative;
    padding-left: 60px;
    margin-bottom: var(--spacing-xl);
}

.timeline-marker {
    position: absolute;
    left: 12px;
    top: 0;
    width: 18px;
    height: 18px;
    border-radius: 50%;
    background-color: var(--color-accent);
    border: 3px solid var(--color-white);
    box-shadow: 0 0 0 3px var(--color-bg-secondary);
}

.timeline-content {
    background-color: var(--color-white);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-base);
}

.timeline-content:hover {
    box-shadow: var(--shadow-lg);
    transform: translateX(4px);
}

.education-header {
    display: flex;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-md);
}

.education-logo {
    width: 48px;
    height: 48px;
    object-fit: contain;
    flex-shrink: 0;
}

.education-title {
    font-size: 1.25rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-text-primary);
    margin-bottom: 0.5rem;
}

.education-institution {
    font-weight: var(--font-weight-semibold);
    color: var(--color-text-secondary);
    margin-bottom: 0.25rem;
}

.education-period {
    color: var(--color-text-tertiary);
    font-size: 0.875rem;
}

.education-status {
    display: inline-block;
    padding: 0.375rem 0.75rem;
    background-color: var(--color-bg-secondary);
    color: var(--color-text-secondary);
    font-size: 0.875rem;
    font-weight: var(--font-weight-medium);
    border-radius: var(--radius-sm);
    margin-top: var(--spacing-sm);
}

.education-detail {
    color: var(--color-text-secondary);
    margin-bottom: 0.5rem;
    line-height: 1.6;
}

/* ===================================
   Footer
   =================================== */
.footer {
    background-color: var(--color-text-primary);
    color: var(--color-white);
    padding: var(--spacing-xl) 0;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.footer-text {
    color: rgba(255, 255, 255, 0.8);
    margin: 0;
}

.footer-links {
    display: flex;
    gap: var(--spacing-md);
}

.footer-link {
    color: var(--color-white);
    transition: all var(--transition-fast);
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    border-radius: var(--radius-sm);
}

.footer-link:hover {
    background-color: var(--color-accent);
    transform: translateY(-2px);
}

/* ===================================
   Animations
   =================================== */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    opacity: 0;
    animation: fadeInUp 0.6s ease-out forwards;
}

/* ===================================
   Responsive Design
   =================================== */
@media (max-width: 1024px) {
    .hero-title {
        font-size: 3.5rem;
    }
    
    .section-title {
        font-size: 2rem;
    }
}

@media (max-width: 768px) {
    :root {
        --spacing-3xl: 4rem;
        --spacing-2xl: 3rem;
    }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .hero-subtitle {
        font-size: 1.25rem;
    }
    
    .section-title {
        font-size: 1.75rem;
    }
    
    .about-text {
        font-size: 1.125rem;
    }
    
    .hero-cta {
        flex-direction: column;
        align-items: stretch;
    }
    
    .btn {
        justify-content: center;
    }
    
    .projects-grid {
        grid-template-columns: 1fr;
    }
    
    .skills-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-content {
        flex-direction: column;
        text-align: center;
    }
    
    .timeline::before {
        left: 10px;
    }
    
    .timeline-item {
        padding-left: 40px;
    }
    
    .timeline-marker {
        left: 2px;
    }
    
    .education-header {
        flex-direction: column;
        text-align: center;
    }
    
    .education-logo {
        align-self: center;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 var(--spacing-md);
    }
    
    .hero-title {
        font-size: 2rem;
    }
    
    .project-footer {
        flex-direction: column;
        gap: var(--spacing-sm);
        align-items: flex-start;
    }
}

/* ===================================
   Utility Classes
   =================================== */
.text-center {
    text-align: center;
}

.mt-1 { margin-top: var(--spacing-xs); }
.mt-2 { margin-top: var(--spacing-sm); }
.mt-3 { margin-top: var(--spacing-md); }
.mt-4 { margin-top: var(--spacing-lg); }

.mb-1 { margin-bottom: var(--spacing-xs); }
.mb-2 { margin-bottom: var(--spacing-sm); }
.mb-3 { margin-bottom: var(--spacing-md); }
.mb-4 { margin-bottom: var(--spacing-lg); }