/* =========================
   外部样式表：styles.css
   用于演示 CSS 的第三种引入方式
   ========================= */

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    font-family: "Microsoft YaHei", "PingFang SC", Arial, sans-serif;
    background-color: #f5f7fb;
    color: #333333;
    line-height: 1.7;
}

.container {
    width: 90%;
    max-width: 1100px;
    margin: 0 auto;
}

.site-header {
    background: linear-gradient(135deg, #1565c0, #42a5f5);
    color: #ffffff;
    padding: 30px 0 20px;
}

.site-header h1 {
    margin: 0 0 10px;
    font-size: 32px;
}

.subtitle {
    margin: 0 0 18px;
    opacity: 0.95;
}

.main-nav {
    margin-top: 10px;
}

.main-nav a {
    display: inline-block;
    color: #ffffff;
    text-decoration: none;
    margin-right: 12px;
    margin-bottom: 10px;
    padding: 8px 14px;
    border: 1px solid rgba(255, 255, 255, 0.35);
    border-radius: 20px;
    transition: 0.3s;
}

.main-nav a:hover {
    background-color: rgba(255, 255, 255, 0.18);
}

.card {
    background-color: #ffffff;
    margin: 24px 0;
    padding: 24px;
    border-radius: 12px;
    box-shadow: 0 4px 14px rgba(0, 0, 0, 0.06);
}

h2 {
    color: #1565c0;
    margin-top: 0;
    border-left: 6px solid #1565c0;
    padding-left: 12px;
}

h3 {
    color: #0d47a1;
    margin-top: 24px;
}

h4 {
    color: #1976d2;
    margin-top: 20px;
}

p, li, dd, dt {
    font-size: 16px;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin: 16px 0 20px;
    background-color: #ffffff;
}

caption {
    caption-side: top;
    text-align: left;
    font-weight: bold;
    margin-bottom: 8px;
    color: #1565c0;
}

table th,
table td {
    border: 1px solid #d6dde8;
    padding: 10px 12px;
    text-align: left;
    vertical-align: top;
}

table th {
    background-color: #eaf3ff;
}

.code-block {
    background-color: #1e1e1e;
    color: #f5f5f5;
    padding: 14px 16px;
    border-radius: 8px;
    overflow-x: auto;
    margin: 14px 0;
}

.flow-box {
    background-color: #eef6ff;
    border: 1px dashed #90caf9;
    padding: 18px;
    border-radius: 10px;
    text-align: center;
    font-weight: bold;
    color: #0d47a1;
}

.arrow {
    display: inline-block;
    margin: 0 8px;
    color: #1565c0;
}

.grid-2 {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 18px;
    margin: 16px 0;
}

.grid-3 {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 18px;
    margin: 16px 0;
}

.method-card {
    background-color: #f8fbff;
    border: 1px solid #d8e8ff;
    border-radius: 10px;
    padding: 16px;
}

.block-demo {
    background-color: #f1f8e9;
    border: 2px solid #8bc34a;
    padding: 16px;
    border-radius: 8px;
    margin: 12px 0;
}

.highlight {
    color: #c62828;
    font-weight: bold;
    background-color: #fff3cd;
    padding: 2px 6px;
    border-radius: 4px;
}

.form-row {
    margin-bottom: 14px;
}

.form-row label {
    margin-right: 10px;
}

input[type="text"],
select,
textarea {
    width: 100%;
    max-width: 420px;
    padding: 10px 12px;
    border: 1px solid #b0bec5;
    border-radius: 6px;
    font-size: 15px;
    outline: none;
}

input[type="text"]:focus,
select:focus,
textarea:focus {
    border-color: #1976d2;
    box-shadow: 0 0 0 3px rgba(25, 118, 210, 0.15);
}

.btn {
    background-color: #1565c0;
    color: #ffffff;
    border: none;
    padding: 10px 18px;
    border-radius: 6px;
    cursor: pointer;
    margin-right: 10px;
    font-size: 15px;
}

.btn:hover {
    background-color: #0d47a1;
}

.btn-secondary {
    background-color: #78909c;
}

.btn-secondary:hover {
    background-color: #546e7a;
}

.external-demo {
    color: #6a1b9a;
    font-size: 17px;
    font-weight: bold;
    border-bottom: 2px dashed #ba68c8;
    display: inline-block;
    padding-bottom: 4px;
}

.box-demo {
    background-color: #fff3e0;   /* content区域背景 */
    padding: 25px;               /* 内边距 */
    border: 8px solid #fb8c00;   /* 边框 */
    margin: 30px 0;              /* 外边距 */
    border-radius: 12px;
    font-weight: bold;
}

.site-footer {
    background-color: #263238;
    color: #ffffff;
    padding: 18px 0;
    margin-top: 30px;
    text-align: center;
}

@media (max-width: 768px) {
    .grid-2,
    .grid-3 {
        grid-template-columns: 1fr;
    }

    .site-header h1 {
        font-size: 26px;
    }

    .main-nav a {
        margin-bottom: 8px;
    }
}