style.css

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

.no-js #loader{
    display: none;
}

.js #loader{
    display: block;
    position: absolute;
    left: 100px;
    top: 0;
}

.card {
    margin-left: 475px;
    margin-top: 20px;
}

.se-pre-con{
    position: fixed;
    left: 0px;
    top: 0px;
    width: 100%;
    height: 100%;
    z-index: 9999;
    background: url(loading.gif) center no-repeat #fff;
}

body{
    background-image: linear-gradient(120deg, #a1c4fd 0%, #c2e9fb 100%);
}

#qr-img{
    width: 200px;
    border-radius: 5px;
    overflow: hidden;
    transition: max-height 1s;
}

#qr-img img{
    width: 100%;
}

#qr-img.show-box{
    max-height: 300px;
    margin: 10px auto;
    padding: 10px;
    border: 1px solid black;
}

.error{
    animation: shake 0.1s linear 10;
}

@keyframes shake{
    0%{
        transform: translateX(0);
    }
    25%{
        transform: translateX(-2px);
    }
    50%{
        transform: translateX(0);
    }
    75%{
        transform: translateX(2px);
    }
    100%{
        transform: translateX(0);
    }
}