/* 
 * Aleksandr Vasilyev Personal Website Styles
 * Optimized for performance, accessibility, and SEO
 * Features: Dark/Light theme system, responsive design, modern layouts
 */

/* ===========================
   CSS Variables for Theme System
   =========================== */
:root {
    /* Light theme colors */
    --color-primary: #1e3a8a;
    --color-primary-light: #3b82f6;
    --color-accent: #0ea5e9;
    --color-accent-hover: #0284c7;
    
    --color-bg: #ffffff;
    --color-bg-secondary: #f8fafc;
    --color-bg-tertiary: #f1f5f9;
    
    --color-text: #1e293b;
    --color-text-secondary: #64748b;
    --color-text-muted: #94a3b8;
    
    --color-border: #e2e8f0;
    --color-shadow: rgba(0, 0, 0, 0.1);
    
    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-mono: 'JetBrains Mono', 'Courier New', monospace;
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-2xl: 4rem;
    
    /* Layout */
    --container-max-width: 1200px;
    --border-radius: 0.5rem;
    --transition: all 0.3s ease;
}

/* Dark theme colors */
[data-theme="dark"] {
    --color-primary: #3b82f6;
    --color-primary-light: #60a5fa;
    --color-accent: #0ea5e9;
    --color-accent-hover: #38bdf8;
    
    --color-bg: #0f172a;
    --color-bg-secondary: #1e293b;
    --color-bg-tertiary: #334155;
    
    --color-text: #f1f5f9;
    --color-text-secondary: #cbd5e1;
    --color-text-muted: #94a3b8;
    
    --color-border: #334155;
    --color-shadow: rgba(0, 0, 0, 0.3);
}

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

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

body {
    font-family: var(--font-primary);
    line-height: 1.6;
    color: var(--color-text);
    background-color: var(--color-bg);
    transition: var(--transition);
}

/* ===========================
   Typography
   =========================== */
h1, h2, h3, h4, h5, h6 {
    font-weight: 600;
    line-height: 1.3;
    margin-bottom: var(--spacing-sm);
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.5rem; }
h4 { font-size: 1.25rem; }

p {
    margin-bottom: var(--spacing-sm);
}

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

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

/* ===========================
   Layout Components
   =========================== */
.container {
    max-width: var(--container-max-width);
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

.section {
    padding: var(--spacing-2xl) 0;
}

.section-title {
    text-align: center;
    margin-bottom: var(--spacing-xl);
    color: var(--color-primary);
    position: relative;
}

.section-title::after {
    content: '';
    display: block;
    width: 60px;
    height: 3px;
    background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
    margin: var(--spacing-sm) auto 0;
    border-radius: 2px;
}

/* ===========================
   Header Styles
   =========================== */
.header {
    background: var(--color-bg);
    border-bottom: 1px solid var(--color-border);
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(10px);
    transition: var(--transition);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md) 0;
}

.name {
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: 0.25rem;
}

.tagline {
    font-size: 1rem;
    color: var(--color-text-secondary);
    font-family: var(--font-mono);
    margin-bottom: 0;
}

.nav {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
}

.nav-links {
    display: flex;
    list-style: none;
    gap: var(--spacing-lg);
}

.nav-link {
    font-weight: 500;
    color: var(--color-text-secondary);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--border-radius);
    transition: var(--transition);
}

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

.theme-toggle {
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: var(--transition);
}

.theme-toggle:hover {
    background-color: var(--color-bg-tertiary);
    transform: scale(1.05);
}

.theme-toggle-icon {
    font-size: 1.2rem;
}

/* ===========================
   About Section
   =========================== */
.about-section {
    background-color: var(--color-bg-secondary);
}

.about-text {
    max-width: 800px;
    margin: 0 auto;
    text-align: center;
}

.intro {
    font-size: 1.2rem;
    font-weight: 500;
    color: var(--color-primary);
    margin-bottom: var(--spacing-lg);
}

/* ===========================
   Skills Section
   =========================== */
.skills-category {
    background: var(--color-bg-secondary);
    padding: var(--spacing-xl);
    border-radius: var(--border-radius);
    border: 1px solid var(--color-border);
    margin-bottom: var(--spacing-xl);
    transition: var(--transition);
}

.skills-category:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px var(--color-shadow);
}

.main-category-title {
    font-size: 1.75rem;
    color: var(--color-primary);
    margin-bottom: var(--spacing-xl);
    text-align: center;
    font-weight: 700;
}

.skill-subcategory {
    margin-bottom: var(--spacing-lg);
    padding: var(--spacing-md);
    background: var(--color-bg);
    border-radius: var(--border-radius);
    border: 1px solid var(--color-border);
}

.skill-subcategory:last-child {
    margin-bottom: 0;
}

.skill-category-title {
    color: var(--color-primary);
    margin-bottom: var(--spacing-md);
    font-family: var(--font-mono);
    font-size: 1.1rem;
    font-weight: 600;
}

.skill-list {
    list-style: none;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-xs) var(--spacing-md);
}

.skill-item {
    padding: var(--spacing-xs) 0;
    color: var(--color-text-secondary);
    position: relative;
    padding-left: var(--spacing-md);
    line-height: 1.5;
}

.skill-item::before {
    content: '▶';
    position: absolute;
    left: 0;
    color: var(--color-accent);
    font-size: 0.8rem;
    top: 0.35rem;
}

/* ===========================
   Projects Section
   =========================== */
.projects-section {
    background-color: var(--color-bg-secondary);
}

.project-card {
    background: var(--color-bg);
    border-radius: var(--border-radius);
    border: 1px solid var(--color-border);
    padding: var(--spacing-xl);
    max-width: 900px;
    margin: 0 auto;
    box-shadow: 0 4px 15px var(--color-shadow);
    transition: var(--transition);
}

.project-card:hover {
    transform: translateY(-3px);
    box-shadow: 0 12px 30px var(--color-shadow);
}

.project-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.project-title {
    font-size: 1.8rem;
    color: var(--color-primary);
    font-family: var(--font-mono);
    margin-bottom: 0;
}

.project-links {
    display: flex;
    gap: var(--spacing-sm);
}

.project-link {
    padding: var(--spacing-xs) var(--spacing-md);
    background: var(--color-accent);
    color: white;
    border-radius: var(--border-radius);
    font-weight: 500;
    transition: var(--transition);
}

.project-link:hover {
    background: var(--color-accent-hover);
    color: white;
    transform: translateY(-1px);
}

.project-description {
    font-size: 1.1rem;
    margin-bottom: var(--spacing-lg);
    color: var(--color-text-secondary);
}

.tech-title,
.features-title {
    font-size: 1rem;
    margin-bottom: var(--spacing-sm);
    color: var(--color-primary);
    font-weight: 600;
}

.tech-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
    margin-bottom: var(--spacing-lg);
}

.tech-tag {
    background: var(--color-bg-tertiary);
    color: var(--color-text);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--border-radius);
    font-size: 0.9rem;
    font-family: var(--font-mono);
    border: 1px solid var(--color-border);
}

.features-list {
    list-style: none;
    padding-left: 0;
}

.features-list li {
    padding: var(--spacing-xs) 0;
    color: var(--color-text-secondary);
    position: relative;
    padding-left: var(--spacing-md);
}

.features-list li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--color-accent);
    font-weight: bold;
}

/* ===========================
   Contact Section
   =========================== */
.contact-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-2xl);
    max-width: 900px;
    margin: 0 auto;
}

.contact-intro {
    font-size: 1.1rem;
    margin-bottom: var(--spacing-lg);
    color: var(--color-text-secondary);
}

.social-links {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.social-link {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm);
    background: var(--color-bg-secondary);
    border-radius: var(--border-radius);
    border: 1px solid var(--color-border);
    transition: var(--transition);
}

.social-link:hover {
    background: var(--color-bg-tertiary);
    transform: translateX(5px);
}

.social-icon {
    font-size: 1.2rem;
}

.contact-form {
    background: var(--color-bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--border-radius);
    border: 1px solid var(--color-border);
}

.form-group {
    margin-bottom: var(--spacing-md);
}

.form-label {
    display: block;
    margin-bottom: var(--spacing-xs);
    font-weight: 500;
    color: var(--color-text);
}

.form-input {
    width: 100%;
    padding: var(--spacing-sm);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    background: var(--color-bg);
    color: var(--color-text);
    font-family: var(--font-primary);
    transition: var(--transition);
}

.form-input:focus {
    outline: none;
    border-color: var(--color-accent);
    box-shadow: 0 0 0 3px rgba(14, 165, 233, 0.1);
}

.form-textarea {
    resize: vertical;
    min-height: 120px;
}

.form-submit {
    width: 100%;
    padding: var(--spacing-md);
    background: var(--color-accent);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: var(--transition);
}

.form-submit:hover {
    background: var(--color-accent-hover);
    transform: translateY(-1px);
}

/* ===========================
   Footer
   =========================== */
.footer {
    background: var(--color-bg-secondary);
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-lg) 0;
}

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

.footer-text {
    color: var(--color-text-muted);
    margin-bottom: 0;
}

.visitor-counter {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.counter-text {
    color: var(--color-text-secondary);
    font-size: 0.9rem;
    font-family: var(--font-mono);
}

.counter-number {
    color: var(--color-accent);
    font-size: 0.9rem;
    font-family: var(--font-mono);
    font-weight: 600;
    background: var(--color-bg-tertiary);
    padding: 2px 8px;
    border-radius: 4px;
    border: 1px solid var(--color-border);
    transition: var(--transition);
}

.counter-number:hover {
    transform: scale(1.05);
    background: var(--color-bg);
}

.counter-badge {
    height: 20px;
    border-radius: 3px;
    transition: var(--transition);
}

.counter-badge:hover {
    transform: scale(1.05);
}

/* ===========================
   Responsive Design
   =========================== */
@media (max-width: 768px) {
    .header-content {
        flex-direction: column;
        gap: var(--spacing-md);
        text-align: center;
    }
    
    .nav {
        flex-direction: column;
        gap: var(--spacing-sm);
    }
    
    .nav-links {
        gap: var(--spacing-md);
    }
    
    .section {
        padding: var(--spacing-xl) 0;
    }
    
    .skill-list {
        grid-template-columns: 1fr;
        gap: var(--spacing-xs);
    }
    
    .skill-subcategory {
        padding: var(--spacing-sm);
    }
    
    .project-header {
        flex-direction: column;
        align-items: flex-start;
    }
    
    .contact-content {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }
    
    .social-links {
        flex-direction: row;
        flex-wrap: wrap;
    }
    
    .footer-content {
        flex-direction: column;
        text-align: center;
        gap: var(--spacing-sm);
    }
    
    h1 { font-size: 2rem; }
    h2 { font-size: 1.75rem; }
}

@media (max-width: 480px) {
    .container {
        padding: 0 var(--spacing-sm);
    }
    
    .nav-links {
        flex-wrap: wrap;
        justify-content: center;
    }
    
    .project-card {
        padding: var(--spacing-lg);
    }
    
    .tech-tags {
        justify-content: center;
    }
    
    h1 { font-size: 1.75rem; }
    h2 { font-size: 1.5rem; }
}

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

.section {
    animation: fadeInUp 0.8s ease-out;
}

/* Smooth scrolling for older browsers */
@media (prefers-reduced-motion: no-preference) {
    html {
        scroll-behavior: smooth;
    }
}