style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
}

.heart-square {
    width: 300px;
    height: 300px;
    background-color: red;
    position: relative;
    transform: rotate(45deg);
    box-shadow: -10px 10px 90px red;
    animation: heart 0.6s linear infinite;
}

@keyframes heart {
    0% {
        transform:  scale(1.07);
    }
    80% {
        transform:  scale(1.0);
    }
    100% {
        transform: scale(0.8);
    }
}

.heart-circle {
    width: 100%;
    height: 100%;
    border-radius: 50%;
    background-color: red;
    box-shadow: -10px -10px 90px red;
    transform: rotate(45deg);
    position: absolute;
}

.heart-circle:nth-of-type(1) {
    top:-50%;
}

.heart-circle:nth-of-type(2) {
    left:-50%;
}