style.css

.triangle {
    width: 0px;
    height: 0x;
    border-left: 30px solid #eeeeee;
    border-top: 15px solid transparent;
    border-bottom: 15px solid transparent;

    float : right;
    margin-top: 9px;
  }

.custom_footer {
    display: flex;
} 

.playBack-container {
    display: flex;
    width: auto;
    justify-content: flex-end;
    height: 20px;
    margin-left: auto;
    margin-right: 100px;
    padding-top: 10px;
}

.playBack-container span{
    color: white;
    margin-left: 30px;
    margin-right: 5px;
}

#playBackRate {
    margin-right: 5px;
    text-align: center;
    width: 30px;
} 

.bookmark {
    position: absolute;
    display: none;
    background-color: #4F4A8D;
    top : 0px;
    right : 0px;
    height: 100%;
    width: 300px;
    padding: 10px;
    overflow: auto;
}

.bookmark .bookmark_close {
    border: none;
    background-color: #4F4A8D;
}

.bookmark .bookmark_remove {
    border: none;
    background-color: #4F4A8D;
    float: right;
    
}

.bookmark .mark{
    color: white;
    padding: 20px 0;
    border-bottom: solid 1px white;
    margin : 7px
}

.bookmark .mark:hover {
    text-decoration: underline;
}

.bookmark .memo{
    font-size: 25px;
}

.bookmark .time{
    color: #dddddd;
}

.triangle:hover {
    -ms-transform: rotate(90deg); 
    -webkit-transform: rotate(90deg); 
    transform: rotate(90deg);
    transition: all 0.5s ease-in;
}