body {
    display: flex;
    height: 100%;
    width: 100%;
    justify-content: center;
    align-items: center;
}

.main {
    display: flex;
    height: 500px;
    width: 500px;
    background-image: repeating-linear-gradient(0, 
    #f4f4f4 0 29px,
    #0c9ff7 29px 30px);
}