Square Illusion

This code snippet was published on .

        
    
<div class="container">
<div class="square square-1"></div>
<div class="square square-2"></div>
<div class="circle circle-1"></div>
<div class="circle circle-2"></div>
<div class="circle circle-3"></div>
<div class="circle circle-4"></div>
</div>
html {
box-sizing: border-box;
}
*,
*:before,
*:after
{
box-sizing: inherit;
}
html,
body
{
height: 100%;
}
body {
background-color: black;
position: relative;
overflow: hidden;
}
.container {
width: 30%;
width: 25vw;
height: 30%;
height: 25vw;
position: absolute;
top: 50%;
left: 50%;
transform: translate3d(-50%, -50%, 0);
cursor: help;
}
.square {
width: 70%;
height: 100%;
position: absolute;
top: 0;
left: 50%;
transform: translateX(-50%);
border-top: 10px solid mediumseagreen;
border-top: 1.5vw solid mediumseagreen;
border-bottom: 10px solid mediumseagreen;
border-bottom: 1.5vw solid mediumseagreen;
animation-duration: 1s;
animation-iteration-count: infinite;
animation-timing-function: linear;
}
.square-1 {
transform: translateX(-50%) rotate(45deg);
animation-name: square-1;
}
.square-2 {
transform: translateX(-50%) rotate(-45deg);
animation-name: square-2;

}
@keyframes square-1 {
0%, 100% {
transform: translateX(-60%) translateY(7%) rotate(45deg);
}
25%, 75% {
transform: translateX(-50%) translateY(0) rotate(45deg);
}
50% {
transform: translateX(-40%) translateY(-7%) rotate(45deg);
}
}

@keyframes square-2 {
0%, 50%, 100% {
transform: translateX(-50%) translateY(0) rotate(-45deg);
}
25% {
transform: translateX(-40%) translateY(7%) rotate(-45deg);
}
75% {
transform: translateX(-60%) translateY(-7%) rotate(-45deg);
}
}

.circle {
background-color: coral;
opacity: 0;
width: 30%;
width: 9vw;
height: 30%;
height: 9vw;
text-align: center;
font-size: 5vw;
line-height: 9vw;
position: absolute;
overflow: hidden;
text-indent: 100%;
border-radius: 50%;
transition: opacity .2s;
animation-duration: 4s;
animation-iteration-count: infinite;
animation-timing-function: linear;
.container:hover &,
.container:focus &
{
opacity: 1;
}
&:hover,
&:focus
{
text-indent: 0;
}
}
.circle-1 {
top: 0;
left: 50%;
transform: translateX(-50%) translateY(-100%);
}
.circle-2 {
bottom: 0;
left: 50%;
transform: translateX(-50%) translateY(100%);
}
.circle-3 {
top: 50%;
left: 0;
transform: translateX(-100%) translateY(-50%);
}
.circle-4 {
top: 50%;
right: 0;
transform: translateX(100%) translateY(-50%);
}

.container:before,
.container:after
{
color: white;
font-size: 3vw;
white-space: nowrap;
position: absolute;
top: 50%;
left: 50%;
transform: translate3d(-50%, -50%, 0);
transition: opacity .5s;
}
.container:before {
content: "Hover me!";
opacity: .8;
}
.container:hover:before {
opacity: 0;
}
.container:after {
content: "Whoa...";
opacity: 0;
}
.container:hover:after {
opacity: .5;
}