body{
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background: linear-gradient(45deg, #cfffd0, #3fff46);
}
.square{
    position: relative;
    width: 300px;
    height: 300px;
    animation: rotate 4s linear infinite;
    border: 30px dashed rgba(0,0,0,.2);
    box-shadow: 0 0 0 30px rgba(0, 0, 0, .5), 
    inset 0 0 0 30px rgba(0, 0, 0, .4)
}
@keyframes rotate{
    0%{
        transform: rotate(360deg);
    }
    100%{
        transform: rotate(0deg);
    }
}
.square span{
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: block;
    overflow: hidden;
}
.square span::before{
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    border: none;
    border-top: 30px solid #fff;
    animation: animate 2s linear infinite;
}
@keyframes animate{
    0%{
        left: -100%;
    }    
    25%{
        left: 0;
    }    
    50%,100%{
        left: 100%;
    }    
}
.square span:nth-child(1){
    transform: rotate(0deg);
}
.square span:nth-child(2){
    transform: rotate(90deg);
}
.square span:nth-child(3){
    transform: rotate(180deg);
}
.square span:nth-child(4){
    transform: rotate(270deg);
}
.square span:nth-child(1)::before{
    animation-delay: 0s;
}
.square span:nth-child(2)::before{
    animation-delay: 0.5s;
}
.square span:nth-child(3)::before{
    animation-delay: 1s;
}
.square span:nth-child(4)::before{
    animation-delay: 1.5s;
}