How to make the block appear smoothly when scrolling down (for example 300px)?

Question

css

Hello.
You need to make it so that when you scroll down the page about 300px down, a block appears at the bottom of the page and is immediately fixed there (right: 30px; bottom: 30px;)

Answer 1

$(window).scroll(function(){
if($(window).scrollTop()>300){
$('#elem').show()
}

})

#elem{
display:none;
position:fixed;
right:30px;
bottom:30px;
}