/* ============================
   GLOBAL RESET & BASE STYLES
   ============================ */

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

:root {
    --primary-color: #000000;
    --secondary-color: #666666;
    --background-color: #FFFFFF;
    --accent-color: #F5F5F5;
    --text-color: #1A1A1A;
    --light-text: #999999;
    --border-color: #E0E0E0;
    --spacing-unit: 8px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    font-size: 16px;
    line-height: 1.7;
    color: var(--text-color);
    background-color: var(--background-color);
    font-weight: 300;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 calc(var(--spacing-unit) * 3);
}

/* ============================
   TYPOGRAPHY
   ============================ */

h1, h2, h3, h4, h5, h6 {
    font-weight: 500;
    line-height: 1.3;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

h1 {
    font-size: 3rem;
    letter-spacing: -0.02em;
}

h2 {
    font-size: 2rem;
}

h3 {
    font-size: 1.5rem;
}

p {
    margin-bottom: calc(var(--spacing-unit) * 2);
}

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

a:hover {
    opacity: 0.6;
}

/* ============================
   HEADER & NAVIGATION
   ============================ */

.header {
    background-color: var(--background-color);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 1000;
    backdrop-filter: blur(10px);
    background-color: rgba(255, 255, 255, 0.95);
}

.nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: calc(var(--spacing-unit) * 3) 0;
}

.logo a {
    font-size: 1.25rem;
    font-weight: 500;
    letter-spacing: -0.01em;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: calc(var(--spacing-unit) * 5);
}

.nav-menu a {
    font-size: 0.95rem;
    font-weight: 400;
    position: relative;
}

.nav-menu a.active::after {
    content: '';
    position: absolute;
    bottom: -4px;
    left: 0;
    width: 100%;
    height: 1px;
    background-color: var(--primary-color);
}

.hamburger {
    display: none;
    flex-direction: column;
    cursor: pointer;
    gap: 5px;
}

.hamburger span {
    width: 24px;
    height: 1px;
    background-color: var(--primary-color);
    transition: var(--transition);
}

/* ============================
   HERO SECTION
   ============================ */

.hero {
    padding: calc(var(--spacing-unit) * 15) 0 calc(var(--spacing-unit) * 12);
    text-align: center;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 400;
    margin-bottom: calc(var(--spacing-unit) * 3);
    letter-spacing: -0.03em;
}

.hero-subtitle {
    font-size: 1.125rem;
    color: var(--secondary-color);
    font-weight: 300;
    max-width: 600px;
    margin: 0 auto;
}

/* ============================
   CATEGORIES
   ============================ */

.categories {
    padding: calc(var(--spacing-unit) * 10) 0;
}

.category-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: calc(var(--spacing-unit) * 3);
}

.category-card {
    padding: calc(var(--spacing-unit) * 6);
    border: 1px solid var(--border-color);
    text-align: center;
    transition: var(--transition);
    cursor: pointer;
}

.category-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.06);
    opacity: 1;
}

.category-card h3 {
    font-size: 1.125rem;
    font-weight: 400;
    margin: 0;
}

/* ============================
   SEARCH SECTION
   ============================ */

.search-section {
    padding: calc(var(--spacing-unit) * 4) 0 calc(var(--spacing-unit) * 8);
}

.search-input {
    width: 100%;
    max-width: 600px;
    margin: 0 auto;
    display: block;
    padding: calc(var(--spacing-unit) * 2) calc(var(--spacing-unit) * 3);
    border: 1px solid var(--border-color);
    font-size: 0.95rem;
    font-family: inherit;
    transition: var(--transition);
    background-color: var(--background-color);
}

.search-input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.search-input::placeholder {
    color: var(--light-text);
}

/* ============================
   ARTICLES GRID
   ============================ */

.articles {
    padding: 0 0 calc(var(--spacing-unit) * 15);
}

.article-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
    gap: calc(var(--spacing-unit) * 6);
    margin-bottom: calc(var(--spacing-unit) * 8);
}

.article-card {
    transition: var(--transition);
    opacity: 1;
}

.article-card.hidden {
    display: none;
}

.article-image {
    width: 100%;
    height: 300px;
    overflow: hidden;
    margin-bottom: calc(var(--spacing-unit) * 3);
}

.article-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: var(--transition);
}

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

.article-category {
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--secondary-color);
    font-weight: 500;
    display: block;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

.article-title {
    font-size: 1.5rem;
    margin-bottom: calc(var(--spacing-unit) * 2);
    font-weight: 500;
}

.article-title a {
    color: var(--text-color);
}

.article-excerpt {
    color: var(--secondary-color);
    margin-bottom: calc(var(--spacing-unit) * 3);
    line-height: 1.6;
}

.article-meta {
    display: flex;
    gap: calc(var(--spacing-unit) * 3);
    font-size: 0.875rem;
    color: var(--light-text);
}

/* ============================
   PAGINATION
   ============================ */

.pagination {
    display: flex;
    justify-content: center;
    gap: calc(var(--spacing-unit) * 2);
    margin-top: calc(var(--spacing-unit) * 8);
}

.pagination-btn {
    padding: calc(var(--spacing-unit) * 1.5) calc(var(--spacing-unit) * 3);
    border: 1px solid var(--border-color);
    background-color: var(--background-color);
    cursor: pointer;
    font-family: inherit;
    font-size: 0.9rem;
    transition: var(--transition);
}

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

.pagination-btn.active {
    background-color: var(--primary-color);
    color: var(--background-color);
    border-color: var(--primary-color);
}

/* ============================
   FOOTER
   ============================ */

.footer {
    background-color: var(--accent-color);
    padding: calc(var(--spacing-unit) * 10) 0 calc(var(--spacing-unit) * 4);
    margin-top: calc(var(--spacing-unit) * 15);
}

.footer-content {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr;
    gap: calc(var(--spacing-unit) * 8);
    margin-bottom: calc(var(--spacing-unit) * 6);
}

.footer-logo {
    font-size: 1.25rem;
    font-weight: 500;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

.footer-section h4 {
    font-size: 0.875rem;
    font-weight: 500;
    margin-bottom: calc(var(--spacing-unit) * 3);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: calc(var(--spacing-unit) * 1.5);
}

.footer-section ul li a {
    color: var(--secondary-color);
    font-size: 0.95rem;
}

.social-icons {
    display: flex;
    gap: calc(var(--spacing-unit) * 2);
}

.social-icons a {
    color: var(--secondary-color);
    transition: var(--transition);
}

.social-icons a:hover {
    color: var(--primary-color);
    opacity: 1;
}

.footer-bottom {
    text-align: center;
    padding-top: calc(var(--spacing-unit) * 4);
    border-top: 1px solid var(--border-color);
    color: var(--secondary-color);
    font-size: 0.875rem;
}

/* ============================
   ANIMATIONS
   ============================ */

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeIn 0.8s ease-out;
}

/* ============================
   ARTICLE DETAIL PAGE
   ============================ */

.article-detail {
    padding: calc(var(--spacing-unit) * 8) 0;
}

.article-header {
    max-width: 800px;
    margin: 0 auto calc(var(--spacing-unit) * 6);
    text-align: center;
}

.article-header h1 {
    font-size: 2.5rem;
    margin-bottom: calc(var(--spacing-unit) * 3);
}

.article-detail-meta {
    display: flex;
    justify-content: center;
    gap: calc(var(--spacing-unit) * 3);
    color: var(--secondary-color);
    margin-bottom: calc(var(--spacing-unit) * 4);
}

.article-body {
    max-width: 800px;
    margin: 0 auto;
}

.article-body img {
    width: 100%;
    height: auto;
    margin: calc(var(--spacing-unit) * 4) 0;
}

.article-body h2 {
    margin-top: calc(var(--spacing-unit) * 6);
    margin-bottom: calc(var(--spacing-unit) * 3);
}

.article-body p {
    margin-bottom: calc(var(--spacing-unit) * 3);
    line-height: 1.8;
}

.product-recommendation {
    background-color: var(--accent-color);
    padding: calc(var(--spacing-unit) * 4);
    margin: calc(var(--spacing-unit) * 6) 0;
}

.product-recommendation h3 {
    margin-bottom: calc(var(--spacing-unit) * 3);
}

.product-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: calc(var(--spacing-unit) * 4);
    margin-top: calc(var(--spacing-unit) * 4);
}

.product-card {
    background-color: var(--background-color);
    padding: calc(var(--spacing-unit) * 3);
    transition: var(--transition);
}

.product-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.06);
}

.product-image {
    width: 100%;
    height: 250px;
    overflow: hidden;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

.product-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.product-name {
    font-weight: 500;
    margin-bottom: calc(var(--spacing-unit) * 1);
    font-size: 1.125rem;
}

.product-description {
    color: var(--secondary-color);
    font-size: 0.9rem;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

.product-link {
    display: inline-block;
    padding: calc(var(--spacing-unit) * 1.5) calc(var(--spacing-unit) * 3);
    border: 1px solid var(--primary-color);
    font-size: 0.875rem;
    transition: var(--transition);
}

.product-link:hover {
    background-color: var(--primary-color);
    color: var(--background-color);
    opacity: 1;
}

/* ============================
   ABOUT & CONTACT PAGES
   ============================ */

.page-header {
    padding: calc(var(--spacing-unit) * 12) 0 calc(var(--spacing-unit) * 6);
    text-align: center;
}

.page-header h1 {
    font-size: 3rem;
    margin-bottom: calc(var(--spacing-unit) * 3);
}

.page-content {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 0 calc(var(--spacing-unit) * 12);
}

.contact-form {
    max-width: 600px;
    margin: calc(var(--spacing-unit) * 6) auto 0;
}

.form-group {
    margin-bottom: calc(var(--spacing-unit) * 4);
}

.form-group label {
    display: block;
    margin-bottom: calc(var(--spacing-unit) * 1.5);
    font-weight: 400;
    font-size: 0.95rem;
}

.form-group input,
.form-group textarea {
    width: 100%;
    padding: calc(var(--spacing-unit) * 2) calc(var(--spacing-unit) * 2.5);
    border: 1px solid var(--border-color);
    font-family: inherit;
    font-size: 0.95rem;
    transition: var(--transition);
}

.form-group textarea {
    min-height: 150px;
    resize: vertical;
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--primary-color);
}

.submit-btn {
    padding: calc(var(--spacing-unit) * 2) calc(var(--spacing-unit) * 6);
    background-color: var(--primary-color);
    color: var(--background-color);
    border: none;
    cursor: pointer;
    font-family: inherit;
    font-size: 0.95rem;
    transition: var(--transition);
}

.submit-btn:hover {
    opacity: 0.8;
}

/* ============================
   RESPONSIVE DESIGN
   ============================ */

@media (max-width: 968px) {
    .category-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .article-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-content {
        grid-template-columns: 1fr;
        gap: calc(var(--spacing-unit) * 6);
    }
}

@media (max-width: 768px) {
    .hamburger {
        display: flex;
    }
    
    .nav-menu {
        position: fixed;
        left: -100%;
        top: 73px;
        flex-direction: column;
        background-color: var(--background-color);
        width: 100%;
        text-align: center;
        transition: 0.3s;
        box-shadow: 0 10px 27px rgba(0, 0, 0, 0.05);
        padding: calc(var(--spacing-unit) * 4) 0;
    }
    
    .nav-menu.active {
        left: 0;
    }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .category-grid {
        grid-template-columns: 1fr;
        gap: calc(var(--spacing-unit) * 2);
    }
    
    .article-header h1 {
        font-size: 2rem;
    }
    
    h1 {
        font-size: 2.5rem;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 calc(var(--spacing-unit) * 2);
    }
    
    .hero {
        padding: calc(var(--spacing-unit) * 8) 0 calc(var(--spacing-unit) * 6);
    }
    
    .hero-title {
        font-size: 2rem;
    }
    
    .hero-subtitle {
        font-size: 1rem;
    }
    
    .product-grid {
        grid-template-columns: 1fr;
    }
}

/* ============================
   BACK TO TOP BUTTON
   ============================ */

.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background-color: var(--primary-color);
    color: var(--background-color);
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transition: var(--transition);
    z-index: 1000;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.back-to-top:hover {
    background-color: var(--secondary-color);
    transform: translateY(-3px);
    box-shadow: 0 6px 16px rgba(0, 0, 0, 0.2);
}

.back-to-top:active {
    transform: translateY(-1px);
}

/* ============================
   READING PROGRESS BAR
   ============================ */

.reading-progress {
    position: fixed;
    top: 0;
    left: 0;
    width: 0%;
    height: 3px;
    background-color: var(--primary-color);
    z-index: 9999;
    transition: width 0.1s ease;
}

/* Mobile adjustments for new features */
@media (max-width: 480px) {
    .back-to-top {
        bottom: 20px;
        right: 20px;
        width: 45px;
        height: 45px;
        font-size: 1.3rem;
    }
    
    .reading-progress {
        height: 2px;
    }
}