body{
    font-family:'Segoe UI',Tahoma,Verdana,sans-serif;
    margin:0;
    padding:0;
    background-color:navy;
    min-height:100vh;
    display:flex;
    flex-direction:column
}
header{
    background-color:navy;
    color:#fff;
    padding:26px;
    text-align:center;
    position:relative
}
header h1{
    margin:0;
    font-size:44px;
    position:relative
}
.header-line{
    border:0;
    border-top:2px solid transparent;
    margin:20px auto;
    width:100px;
    margin-left:49.5%
}
.active{
    position:relative
}
.active::before{
    content:'';
    position:absolute;
    top:-21px;
    left:-18.3px;
    width:200%;
    height:2px;
    background-color:#dc143c
}
nav ul{
    list-style:none;
    padding:0
}
nav ul li{
    display:inline;
    margin-right:20px;
    font-size:22px
}
nav ul li a{
    text-decoration:none;
    color:#fff
}
main{
    padding:20px;
    flex:1;
    display:flex;
    flex-wrap:wrap;
    justify-content:center
}
.course{
    background-color:#fff;
    border:4px solid #ddd;
    border-color:navy;
    padding:20px;
    border-radius:14px;
    margin-bottom:20px;
    width:calc(50% - 20px);
    box-sizing:border-box;
    transition:background-color .3s;
    margin-left:16px;
    margin-right:16px;
}
a{
    text-decoration:none;
    color:inherit;
    text-align:center
}
@media (min-width:768px){
    .course{
        width:calc(50% - 20px)
    }
}
@media (min-width:1024px){
    .course{
        width:calc(33.33% - 20px)
    }
}
@media (max-width:767px){
    .course{
        width:100%
    }
}
footer{
    text-align:center;
    padding:10px;
    background-color:navy;
    color:#fff
}
h2{
    font-size:2.2rem;
    margin-top:0;
    margin-bottom:10px;
    color:navy;
    text-align:center
}
p{
    font-size:1rem;
    line-height:1.6;
    margin-top:18px;
    margin-bottom:20px
}
.dropbtn{
    padding:12px;
    cursor:pointer
}
.dropdown{
    position:relative;
    display:inline-block
}
.dropdown-content{
    display:none;
    position:absolute;
    background-image:linear-gradient(navy,#4682b4);
    box-shadow:0 8px 16px 0 rgba(0,0,0,.2);
    z-index:1;
    border:4px solid;
    border-color:#fff;
    border-radius:16px;
    margin-top:12px
}
.dropdown-content a{
    color:#fff;
    padding:12px 16px;
    text-decoration:none;
    display:block;
    border-radius:14px
}
.dropdown-content a:hover{
    background-color:#dc143c
}
.dropdown:hover .dropdown-content{
    display:block
}
.video-container{
    position:relative;
    padding-bottom:52%;
    overflow:hidden;
    max-width:100%;
    margin-left:20px;
    margin-right: 20px;
    margin-top: 44px;
}
.video-container iframe{
    position:absolute;
    top:0;
    left:0;
    width:100%;
    height:100%;
}