style.css

body {
    background-color: #222;
    color: whitesmoke;
}

#targetKanaDisplay {
    position: relative;
    font-size: 100px;
    font-weight: bolder;
    text-align: center;
    justify-content: center;
    text-shadow: #555 5px 5px;

}

#buttons {
    margin: auto;
    width: 500px;
    display: flex;
    flex-direction: row;
    justify-content: center;
}
.container {
    position: relative;
    padding: 5px;
    cursor: pointer;

    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
  }
  
  /* Hide the default checkbox */
  .container input {
    position: absolute;
    opacity: 0;
    cursor: pointer;
    height: 0;
    width: 0;
  }
  
  /* Create a custom button */
  .button {
    height: 40px;
    width: 25px;
    border: 3px solid whitesmoke;
    font-size: 30pt;
    justify-content: center;
    cursor: pointer;
    text-shadow: #555 2px 2px;
    box-shadow: #555 4px 4px;
  }
  
  /* When container is hovered, change button's styling */
  .container:hover .button {
    background-color: #666;
  }
  
  /* When checkbox is checked, change button's styling */
  .container input:checked + .button {
    position: relative;
    top: -10px;
    color: #90ee90
  }
  
#volume {
  display: flex;
  justify-content: center;
  align-items: center;
}