/* 全局基础重置 */
body, html {
    margin: 0;
    padding: 0;
    height: 100%;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    display: flex;
    flex-direction: column;
    background-color: #f8fafc;
}

/* 顶部 Header 样式 */
header {
    background: #1e293b;
    color: white;
    padding: 15px 20px;
    text-align: center;
}
header h1 { margin: 0 0 5px 0; font-size: 24px; }
header p { margin: 0; font-size: 14px; color: #94a3b8; }

/* Tab 导航栏 */
.tab-nav {
    display: flex;
    background: #334155;
    border-bottom: 2px solid #1e293b;
}
.tab-btn {
    padding: 12px 24px;
    background: none;
    border: none;
    color: #cbd5e1;
    font-size: 15px;
    cursor: pointer;
    transition: background 0.2s;
}
.tab-btn:hover { background: #475569; }
.tab-btn.active {
    background: #f8fafc;
    color: #1e293b;
    font-weight: bold;
}

/* 内容区容器 */
.tab-content {
    flex-grow: 1;
    position: relative;
}
/* iframe 默认隐藏，只有 active 状态的才显示 */
.demo-frame {
    width: 100%;
    height: 100%;
    border: none;
    position: absolute;
    top: 0;
    left: 0;
    display: none;
}
.demo-frame.active { display: block; }