ul {
    list-style: none;
}
.mainContainer {
    display: block;
    width: 100%;
    float: left;
    margin-left: 5%;
    margin-right: auto;
}
.mainContainer:first-child{
    margin-left: auto;
}

.centeredVideo {
    display: block;
    width: 100%;
    height: auto;
    margin-left: auto;
    margin-right: auto;
    margin-bottom: auto;
}

.controls {
    display: block;
    width: 100%;
    text-align: left;
    float: left;
    margin-top: 10px;
    margin-left: auto;
    margin-right: auto;
}
button{
    cursor: pointer;
}

.tanchu{
    display: none;
    margin-top: 20px;
    position: absolute;
    top: 7%;
    left: 15%;
}
.bitton{
    position: absolute;
    left: 40%;
}