#content{
    position: relative;
    width: 100%;
    height: 380px;
}
#thefile {
  position: absolute;
  top: 10px;
  left: 10px;
  z-index: 100;
}

#canvas {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
}

audio {
  position: absolute;
  left: 10px;
  bottom: 10px;
  width: calc(100% - 20px);
}