/* style.css - 终极全设备响应式样式表（四页通用） */
:root {
    --primary-color: #2c3e50;    /* 深蓝色头部 */
    --nav-bg: #1a252f;           /* 深色导航栏 */
    --secondary-color: #e67e22;  /* 橙色高亮 */
    --bg-color: #f4f6f9;         /* 网页背景灰 */
    --success-color: #27ae60;     /* 绿色下载按钮 */
}

* {
    box-sizing: border-box;
}

body {
    font-family: 'PingFang SC', 'Microsoft YaHei', sans-serif;
    margin: 0;
    padding: 0;
    background-color: var(--bg-color);
    color: #333;
    -webkit-text-size-adjust: 100%;
}

/* ==========================================
   1. 公共布局 (头部、导航、容器、底部)
   ========================================== */
header {
    background-color: var(--primary-color);
    color: white;
    padding: 2.5rem 1rem 1.5rem 1rem;
    text-align: center;
}
header h1 {
    margin: 0 0 10px 0;
    font-size: 2.2em;
    letter-spacing: 2px;
}
header p {
    margin: 0;
    font-size: 1.1em;
    color: #ecf0f1;
}

nav {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    background: var(--nav-bg);
    padding: 0.8rem;
}
nav a {
    color: white;
    text-decoration: none;
    margin: 5px 20px;
    font-size: 1.05em;
    font-weight: 500;
    transition: color 0.3s;
}
nav a:hover, nav a.active {
    color: var(--secondary-color);
}

.container {
    max-width: 900px;
    margin: 30px auto;
    padding: 30px;
    background: white;
    box-shadow: 0 4px 10px rgba(0,0,0,0.05);
    border-radius: 8px;
    min-height: 500px;
}

h2 {
    color: var(--primary-color);
    border-left: 4px solid var(--secondary-color);
    padding-left: 12px;
    margin-bottom: 20px;
}

footer {
    text-align: center;
    padding: 20px;
    background: var(--nav-bg);
    color: #7f8c8d;
    margin-top: 40px;
}

/* ==========================================
   2. 课程安排页专属样式 (courses.html)
   ========================================== */
.course-card {
    border: 1px solid #e1e8ed;
    padding: 20px;
    margin-bottom: 20px;
    border-radius: 6px;
    background-color: #fff;
}
.course-card h3 { 
    margin-top: 0; 
    color: var(--primary-color); 
    display: flex;
    align-items: center;
    gap: 10px;
}
.tag { 
    background: #e8f4f8; 
    color: #2980b9; 
    padding: 3px 8px; 
    border-radius: 3px; 
    font-size: 0.75em; 
    font-weight: normal;
}
.btn {
    display: inline-block;
    background-color: var(--secondary-color);
    color: white;
    padding: 10px 20px;
    text-decoration: none;
    border-radius: 4px;
    margin-top: 10px;
    text-align: center;
}
.btn:hover { background-color: #d35400; }

/* ==========================================
   3. 课件下载页专属样式 (downloads.html)
   ========================================== */
.file-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: #fdfdfd;
    border: 1px solid #e1e8ed;
    padding: 15px 20px;
    margin-bottom: 12px;
    border-radius: 5px;
}
.file-name { font-weight: bold; color: #34495e; }
.file-size { color: #95a5a6; font-size: 0.9em; margin-left: 10px; }
.btn-dl { 
    display: inline-block;
    background: var(--success-color); 
    color: white; 
    padding: 8px 16px; 
    border-radius: 4px; 
    text-decoration: none; 
    font-size: 0.9em; 
}
.btn-dl:hover { background: #2ecc71; }

/* ==========================================
   4. 联系反馈页专属样式 (contact.html)
   ========================================== */
.contact-info {
    text-align: center;
    margin-bottom: 30px;
    padding-bottom: 20px;
    border-bottom: 1px solid #eee;
}
.contact-form {
    display: flex;
    flex-direction: column;
    max-width: 600px;
    margin: 0 auto;
}
.contact-form label {
    margin-top: 15px;
    margin-bottom: 5px;
    font-weight: bold;
    color: var(--primary-color);
}
.contact-form input, .contact-form textarea {
    padding: 12px;
    border: 1px solid #ccc;
    border-radius: 4px;
    font-family: inherit;
    font-size: 1em;
}
.contact-form input:focus, .contact-form textarea:focus {
    border-color: var(--secondary-color);
    outline: none;
}
.contact-form button {
    margin-top: 25px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 12px;
    cursor: pointer;
    border-radius: 4px;
    font-size: 1.1em;
    font-weight: bold;
}
.contact-form button:hover { background-color: var(--secondary-color); }


/* ==========================================
   ⚡⚡ 终极多端流式适配（智能媒体查询）
   ========================================== */

/* 针对：平板电脑等中等屏幕 (小于 768px) */
@media (max-width: 768px) {
    .container {
        margin: 15px;
        padding: 20px;
    }
    header h1 {
        font-size: 1.8em;
    }
}

/* 针对：所有智能手机窄屏幕 (小于 480px) */
@media (max-width: 480px) {
    header {
        padding: 1.8rem 1rem 1.2rem 1rem;
    }
    header h1 {
        font-size: 1.5em; /* 确保手机端单行完美显示 */
    }
    header p {
        font-size: 0.95em;
    }

    /* 手机端导航变垂直大按钮，防止误触 */
    nav {
        flex-direction: column;
        padding: 0;
    }
    nav a {
        margin: 0;
        padding: 14px 0;
        width: 100%;
        text-align: center;
        border-bottom: 1px solid rgba(255,255,255,0.05);
    }
    nav a:last-child { border-bottom: none; }

    /* 课程安排页：手机端优化 */
    .course-card {
        padding: 15px;
    }
    .course-card h3 {
        flex-direction: column; /* 手机端标题与“必修”标签上下排，不往右挤 */
        align-items: flex-start;
        gap: 5px;
    }
    .btn {
        width: 100%; /* 手机端进入直播间按钮撑满，极易点击 */
        padding: 12px;
    }

    /* 课件下载页：由横排变竖排，彻底解决大屏变小屏的拥挤问题 */
    .file-item {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
        padding: 15px;
    }
    .file-size {
        display: block;
        margin-left: 0;
        margin-top: 4px;
    }
    .btn-dl {
        width: 100%; /* 手机端下载按钮变成粗大条，方便长按或点击 */
        padding: 12px;
    }

    /* 反馈表单：手机端输入框全面变大 */
    .contact-form input, .contact-form textarea {
        padding: 14px; /* 增大触控面积 */
    }
}