/* ============================================
   我的英语学习笔记 - 主样式文件
   ============================================ */

/* ========== CSS Variables ========== */
:root {
    /* 配色方案 */
    --color-primary: #1a365d;        /* 深蓝色主色调 */
    --color-secondary: #d4af37;      /* 金色点缀 */
    --color-accent: #2d5a87;         /* 浅蓝色 */
    --color-bg: #faf8f3;             /* 米白色背景 */
    --color-white: #ffffff;
    --color-text: #2c3e50;           /* 深灰色文字 */
    --color-text-light: #6c757d;      /* 浅灰色文字 */
    --color-border: #e0e0e0;         /* 边框颜色 */
    
    /* 字体 */
    --font-heading: 'Playfair Display', 'Georgia', serif;
    --font-body: 'Source Sans Pro', 'Arial', sans-serif;
    
    /* 间距 */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-xxl: 4rem;
    
    /* 阴影 */
    --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 8px rgba(0, 0, 0, 0.15);
    --shadow-lg: 0 8px 16px rgba(0, 0, 0, 0.2);
    
    /* 过渡 */
    --transition: all 0.3s ease;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-body);
    font-size: 16px;
    line-height: 1.7;
    color: var(--color-text);
    background-color: var(--color-bg);
    overflow-x: hidden;
}

/* ========== Typography ========== */
h1, h2, h3, h4, h5, h6 {
    font-family: var(--font-heading);
    font-weight: 700;
    line-height: 1.3;
    margin-bottom: var(--spacing-md);
    color: var(--color-primary);
}

h1 {
    font-size: 2.5rem;
}

h2 {
    font-size: 2rem;
}

h3 {
    font-size: 1.5rem;
}

h4 {
    font-size: 1.25rem;
}

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

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

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

/* ========== Header & Navigation ========== */
header {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-accent) 100%);
    color: var(--color-white);
    padding: var(--spacing-lg) 0;
    box-shadow: var(--shadow-md);
    position: sticky;
    top: 0;
    z-index: 1000;
    animation: fadeInDown 0.6s ease;
}

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

.header-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-family: var(--font-heading);
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--color-white);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.logo::before {
    content: "📚";
    font-size: 2rem;
}

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

nav a {
    color: var(--color-white);
    font-weight: 500;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: 4px;
    transition: var(--transition);
}

nav a:hover {
    background-color: rgba(255, 255, 255, 0.2);
    color: var(--color-white);
}

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

/* ========== Hero Section ========== */
.hero {
    background: linear-gradient(135deg, rgba(26, 54, 93, 0.9) 0%, rgba(45, 90, 135, 0.9) 100%),
                url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1200 600"><rect fill="%23faf8f3" width="1200" height="600"/><path d="M0,300 Q300,200 600,300 T1200,300" stroke="%23d4af37" stroke-width="2" fill="none" opacity="0.3"/></svg>');
    background-size: cover;
    background-position: center;
    color: var(--color-white);
    padding: var(--spacing-xxl) var(--spacing-md);
    text-align: center;
    margin-bottom: var(--spacing-xxl);
    animation: fadeIn 0.8s ease;
}

@keyframes fadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

.hero h1 {
    color: var(--color-white);
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
}

.hero p {
    font-size: 1.25rem;
    max-width: 700px;
    margin: 0 auto;
    opacity: 0.95;
}

/* ========== Articles Grid ========== */
.articles-section {
    padding: var(--spacing-xxl) 0;
}

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

.section-title::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 80px;
    height: 3px;
    background: linear-gradient(90deg, var(--color-secondary), var(--color-accent));
    border-radius: 2px;
}

.articles-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-xl);
}

/* ========== Article Card ========== */
.article-card {
    background: var(--color-white);
    border-radius: 12px;
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    transition: var(--transition);
    animation: fadeInUp 0.6s ease;
    animation-fill-mode: both;
}

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

.article-card:nth-child(1) { animation-delay: 0.1s; }
.article-card:nth-child(2) { animation-delay: 0.2s; }
.article-card:nth-child(3) { animation-delay: 0.3s; }
.article-card:nth-child(4) { animation-delay: 0.4s; }
.article-card:nth-child(5) { animation-delay: 0.5s; }
.article-card:nth-child(6) { animation-delay: 0.6s; }

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

.article-card-image {
    width: 100%;
    height: 200px;
    object-fit: cover;
    background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 4rem;
    color: var(--color-white);
}

.article-card-content {
    padding: var(--spacing-md);
}

.article-card-title {
    font-size: 1.5rem;
    margin-bottom: var(--spacing-sm);
    color: var(--color-primary);
}

.article-card-meta {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-sm);
    font-size: 0.9rem;
    color: var(--color-text-light);
}

.article-card-letter {
    display: inline-block;
    width: 32px;
    height: 32px;
    background: var(--color-secondary);
    color: var(--color-primary);
    border-radius: 50%;
    text-align: center;
    line-height: 32px;
    font-weight: 700;
    font-size: 1.1rem;
}

.article-card-description {
    color: var(--color-text-light);
    margin-bottom: var(--spacing-md);
    line-height: 1.6;
}

.article-card-link {
    display: inline-block;
    color: var(--color-accent);
    font-weight: 600;
    padding: var(--spacing-xs) var(--spacing-sm);
    border: 2px solid var(--color-accent);
    border-radius: 6px;
    transition: var(--transition);
}

.article-card-link:hover {
    background-color: var(--color-accent);
    color: var(--color-white);
}

/* ========== Article Detail Page ========== */
.article-header {
    background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
    color: var(--color-white);
    padding: var(--spacing-xxl) var(--spacing-md);
    margin-bottom: var(--spacing-xl);
    text-align: center;
}

.article-header h1 {
    color: var(--color-white);
    font-size: 2.5rem;
    margin-bottom: var(--spacing-sm);
}

.article-meta {
    display: flex;
    justify-content: center;
    gap: var(--spacing-md);
    flex-wrap: wrap;
    margin-top: var(--spacing-md);
    opacity: 0.9;
}

.article-content {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 var(--spacing-md) var(--spacing-xxl);
}

.article-image {
    width: 100%;
    max-width: 600px;
    height: 300px;
    object-fit: cover;
    border-radius: 12px;
    margin: var(--spacing-xl) auto;
    display: block;
    box-shadow: var(--shadow-md);
    background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 5rem;
    color: var(--color-white);
}

.article-section {
    margin-bottom: var(--spacing-xl);
}

.article-section h2 {
    color: var(--color-primary);
    border-left: 4px solid var(--color-secondary);
    padding-left: var(--spacing-md);
    margin-top: var(--spacing-xl);
}

.article-section h3 {
    color: var(--color-accent);
    margin-top: var(--spacing-lg);
}

.highlight-box {
    background: linear-gradient(135deg, rgba(212, 175, 55, 0.1), rgba(45, 90, 135, 0.1));
    border-left: 4px solid var(--color-secondary);
    padding: var(--spacing-md);
    margin: var(--spacing-lg) 0;
    border-radius: 4px;
}

.example-box {
    background: var(--color-white);
    border: 2px solid var(--color-border);
    border-radius: 8px;
    padding: var(--spacing-md);
    margin: var(--spacing-md) 0;
}

.example-box strong {
    color: var(--color-accent);
}

ul, ol {
    margin-left: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
}

li {
    margin-bottom: var(--spacing-xs);
}

/* ========== Footer ========== */
footer {
    background: var(--color-primary);
    color: var(--color-white);
    padding: var(--spacing-xl) var(--spacing-md);
    text-align: center;
    margin-top: var(--spacing-xxl);
}

footer p {
    margin-bottom: var(--spacing-xs);
    opacity: 0.9;
}

.back-to-top {
    display: inline-block;
    margin-top: var(--spacing-md);
    padding: var(--spacing-xs) var(--spacing-md);
    background: var(--color-secondary);
    color: var(--color-primary);
    border-radius: 6px;
    font-weight: 600;
    transition: var(--transition);
}

.back-to-top:hover {
    background: var(--color-white);
    transform: translateY(-2px);
}

/* ========== Responsive Design ========== */
@media (max-width: 768px) {
    :root {
        --spacing-xl: 2rem;
        --spacing-xxl: 3rem;
    }
    
    h1 {
        font-size: 2rem;
    }
    
    h2 {
        font-size: 1.5rem;
    }
    
    .hero h1 {
        font-size: 2rem;
    }
    
    .hero p {
        font-size: 1rem;
    }
    
    .header-container {
        flex-direction: column;
        gap: var(--spacing-md);
    }
    
    nav ul {
        flex-direction: column;
        gap: var(--spacing-sm);
        text-align: center;
    }
    
    .articles-grid {
        grid-template-columns: 1fr;
    }
    
    .article-header h1 {
        font-size: 1.8rem;
    }
    
    .article-meta {
        flex-direction: column;
        gap: var(--spacing-xs);
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 var(--spacing-sm);
    }
    
    .hero {
        padding: var(--spacing-xl) var(--spacing-sm);
    }
    
    .article-content {
        padding: 0 var(--spacing-sm) var(--spacing-xl);
    }
}

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

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