how does jquery fadeIn work? Doing the same with animate()

I love the simple jQuery fadeIn() function, especially because it works without having to set any opacity values to the selector! Just setting it to display:none and using fadeIn() always works.

However I'm not using jQuery for my current project but zepto.js. Zepto only comes with animate() and not with fadeIn().

I wonder how I can create the same behaviour with the animate function! What properties do I have to animate here?

$('#selector').animate({
    display: "block",
    opacity: 1
}, 500, 'ease-out')

Thank you in advance