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;
 }

 body {
     width: 100%;
     background: url('../img/dangki.img/trang.jpg');
     background-size: cover;
 }

 h2 {
     text-align: center;

 }

 form {
     width: 500px;
     margin: 75px 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;
 }

 .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;
 }



 .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;
 }