How to make css animation start on click of button - html

Question

Hi can anyone help me with this tiny thing i don't know how but i want to start animation on a click of button not auto on startup.
h2 {
font-size: 20px;
animation: blurFadeInOut 3s ease-in backwards;
}
h3 {
font-size: 20px;
animation: blurFadeIn 3s ease-in backwards;
}
h2, h3 {
position: absolute;
top: 0;
height: 100%;
margin-top: 0;
width: 100%;
margin-left: 0;
line-height: 69px;
text-align: center;
font-family: "Cedarville Cursive";
color: black;
}
h2.frame-6, h3.frame-1 {
-webkit-animation-delay: 0s;
animation-delay: 0s;
}
h2.frame-7, h3.frame-1 {
-webkit-animation-delay: 11s;
animation-delay: 11s;
}
h2.frame-1, h3.frame-1 {
-webkit-animation-delay: 14s;
animation-delay: 14s;
}
h2.frame-2, h3.frame-2 {
-webkit-animation-delay: 17s;
animation-delay: 17s;
}
h2.frame-3, h3.frame-3 {
-webkit-animation-delay: 20s;
animation-delay: 20s;
}
h2.frame-4, h3.frame-4 {
-webkit-animation-delay: 23s;
animation-delay: 23s;
}
h2.frame-5, h3.frame-5 {
-webkit-animation: none;
animation: none;
}
h2.frame-5 span, h3.frame-5 span {
-webkit-animation: blurFadeIn 2s ease-in 12s backwards;
animation: blurFadeIn 2s ease-in 12s backwards;
color: transparent;
text-shadow: 0px 0px 1px #fff;
}
#-webkit-keyframes blurFadeInOut{
0%{
opacity: 0;
text-shadow: 0px 0px 40px #fff;
transform: scale(1.3);
}
20%,75%{
opacity: 1;
text-shadow: 0px 0px 1px #fff;
transform: scale(1);
}
100%{
opacity: 0;
text-shadow: 0px 0px 50px #fff;
transform: scale(0);
}
}
#-webkit-keyframes blurFadeIn{
0%{
opacity: 0;
text-shadow: 0px 0px 40px #fff;
transform: scale(1.3);
}
50%{
opacity: 0.5;
text-shadow: 0px 0px 10px #fff;
transform: scale(1.1);
}
100%{
opacity: 1;
text-shadow: 0px 0px 1px #fff;
transform: scale(1);
}
}
enter code here
<center><h2 class='frame-6'>Because today is a special day, sending birthday wishes simply wouldn’t do, so I’m sending you a day when all of your dreams come true, and a year that means the most to you!</h2></center>
<center><h2 class='frame-7'>Let's sing together!</h2></center>
<center><h2 class='frame-1'>Happy Birthday Too You</h2></center>
<center> <h2 class='frame-2'>Happy Birthday Too You</h2></center>
<center> <h2 class='frame-3'>Happy Birthday Dear Demo</h2></center>
<center> <h2 class='frame-4'>Happy Birthday Toooo Youuuu</h2></center>
<h3 class='frame-5'><span><h2 class='frame-3'>Wish You A Verry Happy Birthday Demo </h2></span></h3>