fade in a page works well and slidedown doesn't work

fade in a page works well and slidedown doesn't work

I have 2 pages when button in page1 is clicked it will linked to the page
2, then the page2 will load with transition. The page loads with fade in
and doesnt work with slidedown.
$(document).ready(function() {
$("body").css("display", "none");
$("body").fadeIn(2000);
});
The code about works well,but the below doesnt work:
$(document).ready(function() {
$("body").css("display", "none");
$("body").slideDown(2000);
});