Audio that plays in the background:
<audio autoplay id="myaudio">
<source src="https://ia801707.us.archive.org/27/items/just-like-heaven/09%20-%20Just%20Like%20Heaven.mp3">
</audio>
<script>
var audio = document.getElementById("myaudio");
audio.volume = 0.1;
</script>
To change the volume, adjust the audio.volume value.