Is it possible to style html5 audio tag?

I haven't found any resources on how to do that. Something as simple as changing the color of the player would be nice to have :)

Yes: you can hide the built-in browser UI (by removing the controls attribute from audio) and instead build your own interface and control the playback using Javascript (source):

<audio id="player" src="vincent.mp3"></audio>
<div> 
  <button onclick="document.getElementById('player').play()">Play</button> 
  <button onclick="document.getElementById('player').pause()">Pause</button> 
  <button onclick="document.getElementById('player').volume += 0.1">Vol +</button> 
  <button onclick="document.getElementById('player').volume -= 0.1">Vol -</button> 
</div>

You can then style the elements however you wish using CSS.

MDN HTMLAudioElement API reference

<audio>

audio::-webkit-media-controls-panel

audio::-webkit-media-controls-mute-button

audio::-webkit-media-controls-play-button

audio::-webkit-media-controls-timeline-container

audio::-webkit-media-controls-current-time-display

audio::-webkit-media-controls-time-remaining-display

audio::-webkit-media-controls-timeline

audio::-webkit-media-controls-volume-slider-container

audio::-webkit-media-controls-volume-slider

audio::-webkit-media-controls-seek-back-button

audio::-webkit-media-controls-seek-forward-button

audio::-webkit-media-controls-fullscreen-button

audio::-webkit-media-controls-rewind-button

audio::-webkit-media-controls-return-to-realtime-button

audio::-webkit-media-controls-toggle-closed-captions-button

REFERENCE: https://chromium.googlesource.com/chromium/blink/+/72fef91ac1ef679207f51def8133b336a6f6588f/Source/core/css/mediaControls.css?autodive=0%2F%2F%2F

Yes! The HTML5 audio tag with the "controls" attribute uses the browser's default player. You can customize it to your liking by not using the browser controls, but rolling your own controls and talking to the audio API via javascript.

Luckily, other people have already done this. My favorite player right now is jPlayer, it is very stylable and works great. Check it out.

The appearance of the tag is browser-dependent, but you can hide it, build your own interface and control the playback using Javascript.

some color tunings

audio {
    filter: sepia(20%) saturate(70%) grayscale(1) contrast(99%) invert(12%);
    width: 200px;
    height: 25px;
}

Ken had it right as well.

a css tag:

audio {

}

will get you some results. seems it doesnt want the player any height above or below 25px but the width can be shortened or lengthened to an extent.

this was good enough for me; see this example (warning, audio plays automatically): www.thenewyorkerdeliinc.com

Missing the most important one IMO the container for the controls ::-webkit-media-controls-enclosure:

&::-webkit-media-controls-enclosure {
	border-radius: 5px;
    background-color: green;
}

To change just the colour of the player, simply address the audio tag in your css file, for instance on one of my sites the player became invisible (white on white) so I added:

audio {
    background-color: #95B9C7;
}

This changed the player to light blue.

Yes, it's possible, from @Fábio Zangirolami answer

audio::-webkit-media-controls-panel, video::-webkit-media-controls-panel {
			    background-color: red;
}

If you are using Chrome, turned on "Show user agent shadow DOM" in Chrome Dev Tool settings

Now you'll able to see all the pseudos

audio::-webkit-media-controls-panel

audio::-webkit-media-controls-mute-button

audio::-webkit-media-controls-play-button

...

and now you can style them

audio::-webkit-media-controls-mute-button {
  display: none;
}

I did some customizations on the Audio component. Here is what i did.

audio {
/*border-radius: 90px;*/
width: 250px;
height: 45px;
margin-top: 5px;
margin-bottom: 5px;
}

audio::-webkit-media-controls-mute-button {
display: none !important;
}

audio::-webkit-media-controls-volume-slider {
display: none !important;
}

audio::-webkit-media-controls-volume-control-container.closed {
display: none !important;
}
audio::-webkit-media-controls-volume-control-container{
display: none !important;
}

I found that these customizations only works for Edge and Chrome. Not Firefox..

You can use HTMLMediaElement Api to create your own audioplayer with html/css. It is likely the only option. Because the default player can't be styled.

If you want to style the browsers standard music player in the CSS:

audio {
    enter code here;
}