Pulsating ring animation with CSS - html

Question

I want to have an expanding radius that starts from the center of the div instead of it starting on the top left of the div.
Imagine the button has a pulsing outline that goes outwards. That pulsing outline should start from the middle of the div and go out.
See example here: https://jsbin.com/dinehoqaro/edit?html,css,output
You can see that the expansion is starting from the top left.
.circle {
background-color: white;
border: 1px solid red;
border-radius: 50%;
width: 50px;
height: 50px;
animation: pulse 1s infinte;
-webkit-animation: pulse 1.2s infinite;
}
button {
background-color: green;
border: none;
border-radius: 50%;
width: 50px;
height: 50px;
}
#-webkit-keyframes pulse {
from {
width: 50px;
height: 50px;
}
to {
width: 100px height: 100px;
}
}
#keyframes pulse {
from {
width: 50px;
height: 50px;
}
to {
width: 100px;
height: 100px;
}
}
<div class="circle"><button>click here</button></div>

Answer 1

Here's a general solution using CSS flexbox, transform and pseudo-elements.
body {
display: flex;
align-items: center;
justify-content: center;
background-color: lightyellow;
height: 100vh;
margin: 0;
}
#container {
display: flex;
align-items: center;
justify-content: center;
}
.sphere {
display: flex;
background: lightblue;
border-radius: 300px;
height: 100px;
width: 100px;
}
#container::after {
display: flex;
background: lightpink;
border-radius: 300px;
height: 250px;
width: 250px;
animation: pulsate 2.5s ease-out;
animation-iteration-count: infinite;
opacity: 0.0;
content: "";
z-index: -1;
margin: auto;
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
}
#keyframes pulsate {
0% {
transform: scale(0.1, 0.1);
opacity: 0.0;
}
50% {
opacity: 1.0;
}
100% {
transform: scale(1.2, 1.2);
opacity: 0.0;
}
}
<div id="container">
<div class="sphere"></div>
</div>
jsFiddle
Also see this awesome solution by #harry: How to create a pulsing glow ring animation in CSS?