/* -------- 全局设置 -------- */
body {
    font-family: "Inter", "Microsoft YaHei", sans-serif;
    margin: 0;
    background: linear-gradient(145deg, #f7faff 0%, #ecf4ff 100%);
    color: #2e3a59;
    line-height: 1.6;
}

/* -------- 导航栏 -------- */
header {
    background: rgba(62, 112, 255, 0.95);
    backdrop-filter: blur(8px);
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
    position: sticky;
    top: 0;
    z-index: 1000;
}

nav ul {
    display: flex;
    justify-content: center;
    align-items: center;
    list-style: none;
    margin: 0;
    padding: 1rem 0;
    gap: 30px;
}

nav a {
    color: #fff;
    font-weight: 600;
    text-decoration: none;
    position: relative;
}

nav a::after {
    content: "";
    position: absolute;
    left: 0;
    bottom: -5px;
    width: 0%;
    height: 2px;
    background-color: #ffe58a;
    transition: width 0.3s ease;
}

nav a:hover::after {
    width: 100%;
}

/* -------- 主体内容 -------- */
main {
    max-width: 1000px;
    margin: 60px auto 80px;
    text-align: center;
    padding: 0 25px;
}

h1 {
    font-size: 2.6em;
    background: linear-gradient(90deg, #3e70ff, #7b97ff);
    -webkit-background-clip: text;
    color: transparent;
    margin-bottom: 0.6em;
}

h2 {
    color: #555;
    font-weight: 400;
    margin-bottom: 2em;
}

/* -------- 课程卡片区域 -------- */
.courses {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
    gap: 30px;
    margin-top: 40px;
}

.course {
    background: white;
    border-radius: 14px;
    box-shadow: 0 6px 20px rgba(0,0,0,0.08);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    overflow: hidden;
}

.course:hover {
    transform: translateY(-6px);
    box-shadow: 0 10px 25px rgba(62,112,255,0.15);
}

.course a {
    display: block;
    text-decoration: none;
    color: #3e70ff;
    font-weight: 600;
    padding: 30px 25px;
}

.course a:hover {
    color: #2c50cc;
}

/* -------- 按钮样式 -------- */
.button {
    display: inline-block;
    margin-top: 40px;
    background: linear-gradient(90deg, #3e70ff, #6ea3ff);
    color: white;
    padding: 14px 30px;
    border-radius: 10px;
    text-decoration: none;
    font-weight: 600;
    letter-spacing: 0.5px;
    transition: box-shadow 0.3s ease, transform 0.3s ease;
}

.button:hover {
    transform: translateY(-3px);
    box-shadow: 0 6px 15px rgba(62,112,255,0.3);
}

/* -------- 页脚 -------- */
footer {
    background: #3e70ff;
    color: #fff;
    text-align: center;
    font-size: 0.9em;
    padding: 20px 10px;
    letter-spacing: 0.3px;
    box-shadow: 0 -3px 12px rgba(0,0,0,0.05);
}