#link1:hover{
    background-color: orange;
    cursor: pointer;
}
@media only screen and (max-width:768px){
    h1{
        font-size: 20px;
    }
    #video{
        width: 480px;
    }
    #bd{
        width: 400px;
    }
}
#btnon{
    margin-left: 70px;
}
#btnoff{
    margin-left: 50px;
}
.slider {
    width: 100%;
    height: auto;
    overflow: hidden;
}
.slide {
    width: 100%;
    height: 100%;
    animation: fade 9s linear infinite;
}
@keyframes fade {
    0% {opacity: 0;}
    20% {opacity: 1;}
    80% {opacity: 1;}
    100% {opacity: 0;}
}
#slide1 { animation-delay: 0s; }
#slide2 { animation-delay: 0s; display: none; }
#slide3 { animation-delay: 0s; display: none; }
#slide4 { animation-delay: 0s; display: none; }
.arrow {
    text-decoration: none;
    display: flex;
    justify-content: center;
    align-items: center;
    width: 50px;
    height: 50px;
    background-color: rgba(0, 0, 0, 0.5);
    color: white;
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    z-index: 1000;
}  
.arrow-prev {
    left: 10px;
}
.arrow-next {
    right: 10px;
}
#thongbao{
	margin:0px auto;
	text-align: center;
}