.btn {
    width:75px;
}
.imageTumbnail {
    height:300px;
    width:auto;
}

body {
    background-color: #f7f7f7;
    line-height: 2;
}


.book-container {
    max-width: 800px;
    background: #ffffff;
    border-radius: 16px;
    padding: 30px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}


.word {
    color: rgba(0, 0, 0, 0.20); /* almost invisible black */
    filter: blur(4px); /* slight blur */
    transition: 0.25s;
    cursor: pointer;
}


    .word.visible {
        color: #212529;
        filter: blur(0);
    }