*{
    margin:0;
    padding:0;
    box-sizing:border-box;
}

body{
    font-family:"Times New Roman", serif;
}

.menu{

    width:900px;
    margin:40px auto;
    background:#00008B;
    list-style:none;

    display:flex;
}

.menu>li{

    position:relative;
}

.menu>li>a{

    display:block;
    width:180px;
    text-align:center;

    color:#FFD700;
    text-decoration:none;

    padding:15px 0;

    font-size:28px;
    font-weight:bold;
}

/* Hover menu chính */

.menu>li:hover>a{

    background:#ADFF2F;
    color:black;
}

/* Menu con */

.submenu{

    position:absolute;

    top:100%;
    left:0;

    list-style:none;

    display:none;

    width:180px;

    background:#00008B;
}

/* Hiện menu con */

.menu li:hover .submenu{

    display:block;
}

/* Item menu con */

.submenu li a{

    display:block;

    color:#FFD700;

    text-decoration:none;

    padding:15px;

    font-size:22px;
}

/* Hover menu con */

.submenu li a:hover{

    background:lightblue;
    color:black;
}
.back{
    text-align:center;
    padding-top:250px;
}

.back a{

    display:inline-block;

    padding:12px 25px;

    background:linear-gradient(135deg,#4CAF50,#2E8B57);

    color:white;

    text-decoration:none;

    border-radius:30px;

    font-size:18px;

    font-weight:bold;

    box-shadow:0 5px 10px rgba(0,0,0,.2);

    transition:.3s;
}

.back a:hover{

    background:linear-gradient(135deg,#2E8B57,#4CAF50);

    transform:translateY(-3px);

    box-shadow:0 8px 18px rgba(0,0,0,.3);
}