.audio-control {
    position: fixed;
    bottom: 20px;
    right: 20px;
    z-index: 1000;
    touch-action: manipulation; /* タッチ操作の最適化 */
}

.speaker {
    height: 60px;
    width: 60px;
    position: relative;
    overflow: hidden;
    display: inline-block;
    cursor: pointer;
    background: rgba(0, 0, 0, 0.6);
    border-radius: 50%;
    padding: 15px;
}

.speaker span {
    display: block;
    width: 0px;
    height: 0px;
    background: #fff;
    margin: 11px 0 0 2px;
}

.speaker span:after {
    content: '';
    position: absolute;
    width: 0;
    height: 0;
    border-style: solid;
    border-color: transparent #fff transparent transparent;
    border-width: 15px 21px 15px 22px;
    left: -15px;
    top: 15px;
}

.speaker span:before {
    transform: rotate(45deg);
    border-radius: 0 50px 0 0;
    content: '';
    position: absolute;
    width: 7px;
    height: 7px;
    border-style: double;
    border-color: #fff;
    border-width: 10px 10px 0 0;
    left: 30px;
    top: 20px;
    transition: all 0.2s ease-out;
}

.speaker:hover span:before {
    transform: scale(.8) translate(-3px, 0) rotate(42deg);
}

.speaker.mute span:before {
    transform: scale(.5) translate(-15px, 0) rotate(36deg);
    opacity: 0;
}

.speaker:hover {
    background: rgba(0, 0, 0, 0.8);
}