*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body{
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: #000;
}
.loader{
    position: relative;
    width: 200px;
    height: 200px;
    overflow: hidden;
    -webkit-box-reflect: below 1px linear-gradient(transparent, #0005);
}
.loader:hover{
    background: #03e9f4;
    box-shadow: 0 0 5px #03e9f4,
                0 0 25px #03e9f4,
                0 0 50px #03e9f4,
                0 0 200px #03e9f4;
}
.loader span{
    position: absolute;
    display: block;
}
/* ----------------------------- */
.loader span:nth-child(1){
    top: 0;
    left: -100%;
    width: 100%;
    height: 40px;
    background: linear-gradient(90deg, transparent, #03e9f4);
    animation: animate1 1s linear infinite;
    animation-delay: 0s;
}
@keyframes animate1{
    0%{
        left: -100%;
    }
    100%{
        left: 100%;
    }
}
/* ------------------------------ */
.loader span:nth-child(3){
    bottom: 0;
    left: -100%;
    width: 100%;
    height: 40px;
    background: linear-gradient(270deg, transparent, #03e9f4);
    animation: animate3 1s linear infinite;
    animation-delay: 0s;
}
@keyframes animate3{
    0%{
        left: 100%;
    }
    100%{
        left: -100%;
    }
}
/* ---------------------------- */
.loader span:nth-child(2){
    right: 0;
    top: -100%;
    width: 40px;
    height: 100%;
    background: linear-gradient(180deg, transparent, #03e9f4);
    animation: animate2 1s linear infinite;
    animation-delay: 0.5s;
}
@keyframes animate2{
    0%{
        top: -100%;
    }
    100%{
        top: 100%;
    }
}
/* ---------------------------- */
.loader span:nth-child(4){
    left: 0;
    top: -100%;
    width: 40px;
    height: 100%;
    background: linear-gradient(0deg, transparent, #03e9f4);
    animation: animate4 1s linear infinite;
    animation-delay: 0.5s;
}
@keyframes animate4{
    0%{
        top: 100%;
    }
    100%{
        top: -100%;
    }
}