show and hide hidden div in javascript with animation from sec code example

Example 1: js hide div

//If you have jquery, you can use the following method:
$("#mydiv").hide(); //hides div.
$("#mydiv").show(); //shows div.
//If you don't have jquery...
//search up the following: html how to add jquery

Example 2: how to hide div in html

document.getElementById('elementName').hide();