body{
    font-family: Tahoma, sans-serif;
    margin: 0;
}

.top-nav{
    background:#1e3a8a;
    padding:12px 0;
    margin-bottom:30px;
}

.nav-inner{
    max-width:1100px;
    margin:0 auto;
    padding:0 20px;
}

.nav-inner a{
    display:inline-block;
    color:#fff;
    text-decoration:none;
    margin-right:14px;
    padding:10px 14px;
    border-radius:6px;
}

.nav-inner a:hover{
    background:rgba(255,255,255,.15);
}

.khoi{
    margin: 0 30px 60px;
}

h2{
    margin-top: 50px;
    margin-bottom: 20px;
}

.tieu-de-phu{
    margin-top: 50px;
}

/* ================= BÀI 1 ================= */
.menu-ngang{
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    width: max-content;
}

.menu-ngang li{
    margin-right: 2px;
}

.menu-ngang li a{
    display: block;
    padding: 15px 30px;
    background: blue;
    color: white;
    text-decoration: none;
}

.menu-ngang li a:hover{
    background: oldlace;
    color: black;
}

/* ================= BÀI 2.1 - MENU DỌC CẤP 2 ================= */
#menu-cap2,
#menu-cap2 ul{
    list-style: none;
    padding: 0;
    margin: 0;
}

#menu-cap2{
    width: 150px;
    position: relative;
}

#menu-cap2 li{
    width: 150px;
    background: #000000;
    border-bottom: 1px solid #FFF;
    position: relative;
}

#menu-cap2 li a{
    display: block;
    padding: 12px;
    color: #FFF;
    text-decoration: none;
}

#menu-cap2 li:hover > a{
    background: darkgray;
}

#menu-cap2 li ul{
    display: none;
    position: absolute;
    top: 0;
    left: 150px;
    width: max-content;
    min-width: 180px;
}

#menu-cap2 li ul li{
    width: auto;
    white-space: nowrap;
}

#menu-cap2 li:hover > ul{
    display: block;
}

/* ================= BÀI 2.2 - MENU DỌC CẤP 3 ================= */
#menu-cap3,
#menu-cap3 ul{
    list-style: none;
    padding: 0;
    margin: 0;
}

#menu-cap3{
    width: 150px;
    position: relative;
    margin-top: 40px;
}

#menu-cap3 li{
    width: 150px;
    background: #000000;
    border-bottom: 1px solid #FFF;
    position: relative;
}

#menu-cap3 li a{
    display: block;
    padding: 12px;
    color: #FFF;
    text-decoration: none;
}

#menu-cap3 li:hover > a{
    background: darkgray;
}

#menu-cap3 li ul{
    display: none;
    position: absolute;
    top: 0;
    left: 150px;
    width: max-content;
    min-width: 160px;
}

#menu-cap3 li ul li{
    width: auto;
    white-space: nowrap;
}

#menu-cap3 li ul li ul{
    top: 0;
    left: 100%;
    width: max-content;
}

#menu-cap3 li:hover > ul{
    display: block;
}

/* ================= BÀI 3 - MENU NGANG ĐA CẤP ================= */
.menu-da-cap,
.menu-da-cap ul{
    list-style: none;
    padding: 0;
    margin: 0;
}

.menu-da-cap{
    width: max-content;
    display: flex;
    background: blue;
}

.menu-da-cap > li{
    position: relative;
}

.menu-da-cap a{
    display: block;
    padding: 12px 18px;
    background: blue;
    color: white;
    text-decoration: none;
    border-right: 1px solid white;
    white-space: nowrap;
}

.menu-da-cap li:hover > a{
    background: oldlace;
    color: black;
}

.menu-da-cap li ul{
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    min-width: max-content;
}

.menu-da-cap li ul li{
    position: relative;
}

.menu-da-cap li ul li ul{
    top: 0;
    left: 100%;
}

.menu-da-cap li:hover > ul{
    display: block;
}

.menu-da-cap li ul a{
    border-top: 1px solid white;
    border-right: none;
}