header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            background: #fff;
            padding: 40px 30px;
            box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
            position: sticky;
            top: 0;
            z-index: 100;
        }

        .logo img {
            height: 50px;
        }

        /* menu chính */
        .menu {
            list-style: none;
            display: flex;
            margin: 0 auto;
            align-items: center;
        }

        .menu>li {
            position: relative;
        }

        .menu a {
            white-space: nowrap;
            text-decoration: none;
            color: #333;
            font-weight: 600;
            padding: 8px;
            font-size: large;
            justify-content: space-between;
            display: flex;
            width: 200px;
        }

        .menu a:hover {
            color: #ff9900;
        }

        /* submenu */
        .submenu {
            list-style: none;
            position: absolute;
            top: 100%;
            left: 0;
            background: #fff;
            padding: 10px 0;
            min-width: 150px;
            display: none;
            box-shadow: 0 2px 6px rgba(0, 0, 0, 0.15);

        }

        .submenu li a {
            display: block;
            padding: 8px 15px;
            color: #333;
        }

        .submenu li a:hover {
            background: #f1f1f1;
            color: #ff9900;
        }

        .menu li:hover .submenu {
            display: block;
        }
        *{
            
            padding: 0;
            margin: 0;
            box-sizing: border-box;
        }
        h2{
            text-align: center;
        }
        body {
            background: url('../img/dangki.img/trang.jpg');
            background-size: cover;
            
        }

        form {
            width: 500px;
            margin: 50px auto; 
            box-shadow: 0 0 5px gray;
            padding: 10px;
            font-size: 14px;
            font-family: Arial, sans-serif;
        }

        .form-gruop {
            padding: 10px;

        }

        .form-gruop label {
            line-height: 30px;
        }

        .form-control {
            width: 100%;
            height: 30px;
            border-radius: 5px;
            border: 1px solid gray;
            outline: none;
            padding-left: 5px;
            font-size: 16px;
        }

        .form-control:focus {
            border: 1px solid black;
            background-color: white;
        }
        .but {
            display: block;
            width: 100%;
            /* chiếm toàn bộ chiều ngang */
            padding: 15px 0;
            /* khoảng cách trên dưới */
            background-color: #3a3a3a;
            /* màu xám đậm */
            color: white;
            /* chữ trắng */
            font-weight: bold;
            /* chữ đậm */
            text-transform: uppercase;
            /* viết hoa toàn bộ */
            border: none;
            /* bỏ viền */
            border-radius: 6px;
            /* bo nhẹ các góc */
            cursor: pointer;
            /* đổi con trỏ khi rê chuột */
            transition: background 0.3s;
        }
         .quen {
     font-size: larger;
     color: red;
     justify-content: space-between;
     display: flex;

 }

 .quen>a {
     color: black;
     text-decoration: none;

 }

 .quen>a:hover {
     color: rgba(255, 8, 0, 0.911);
     text-decoration: underlinea;
 }