style.css

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

html {
    font: clamp(0.9rem, 1.5vw, 0.98rem)/1.44 Georgia, serif;
    background-color: hsl(25, 100%, 92%);
    color: hsl(25, 50%, 5%);
}

body {
    width: min(90rem, 100%);
    margin: 0 auto;
    padding: 1em 0.8em;
    overflow-x: hidden;
}

/* ************************** BOOK MOBILE DISPLAY ********************* */
.bookmat {
    box-sizing: content-box;
    position: relative;
}

.preface {
    margin: 2em 0.3rem;
    font: 0.9em/1.44 Georgia, serif;
}

.book {
    position: relative;
    font: 0.8em/1.2 Georgia, serif;
    background-color: hsl(20, 50%, 95%);
    box-shadow: 0 0.5em 20px rgba(0, 0, 0, 0.3);
}

.book::before {
    content: '‹';
    position: absolute;
    padding: 0 0.4em 0.13em;
    top: -0.07em;
    right: -0.2em;
    font-size: 12em;
    line-height: 1;
    color: hsla(20, 50%, 35%, 0.2);
    transform: rotate(0deg);
    transition: transform 0.5s;
}

.bookpage {
    pointer-events: none;
    color: hsl(20, 50%, 15%);
    background-color: hsl(20, 50%, 95%);
    padding: 0.4em;
    margin-bottom: -2em;
    line-height: 0;
    opacity: 0;
    transition: line-height 0.5s 0.6s, opacity 1s, margin-bottom 0.5s 0.6s;
}

.front.cover {
    margin-bottom: 0;
    line-height: 1.2;
    opacity: 1;
}

.bookpage p,
.bookpage footer {
    padding: 0.3em 2em;
    hyphens: auto;
    text-align: justify;
}

.bookpage p {
    pointer-events: none;
}

.bookpage .booktitle {
    font-size: 2em;
    text-align: left;
}

.pagetext::first-letter {
    font-size: 2em;
}

.unrolled.book::before {
    transform: rotate(-90deg);
}

.unrolled.book>.bookpage {
    line-height: 1.2;
    margin-bottom: 0;
    opacity: 1;
    transition: line-height 1s, opacity 0.5s 0.6s, margin-bottom 1s;
}

/* ************************** BOOK MOBILE RTL ********************* */
.rtl .bookpage .booktitle {
    text-align: right;
}

.rtl .book::before {
    left: -0.2em;
    right: auto;
    transform: rotate(180deg);
}

.rtl .unrolled.book::before {
    transform: rotate(270deg);
}

@media (min-width:700px) {

    /* ************************** BOOK DESKTOP DISPLAY ********************* */
    .bookmat {
        display: flex;
        align-items: center;
        min-height: 30rem;
    }

    .preface {
        width: 25%;
        margin: 0 5%;
        pointer-events: none;
    }

    .book {
        counter-reset: pagecounter;
        position: absolute;
        pointer-events: none;
        top: 0;
        bottom: 0;
        left: 0;
        right: 0;
        margin: auto;
        width: 60%;
        height: 90%;
        perspective: 75rem;
        /* transform: rotate(20deg) scale(0.5); */
        /* transition: transform 1s 3s; */
        background-color: transparent;
        box-shadow: none;
    }

    .opened.book {
        transform: rotate(0);
        transition: transform 3s;
    }

    .book::before {
        content: none;
    }

    .bookpage {
        counter-increment: pagecounter;
        position: absolute;
        top: 0.5em;
        bottom: 0.5em;
        margin: 0;
        padding: 0;
        width: 50%;
        line-height: 1.2;
        opacity: 1;
        backface-visibility: hidden;
        cursor: pointer;
        user-select: none;
        box-shadow: inset 3px 0px 20px rgba(0, 0, 0, 0.1);
        transform-style: preserve-3d;
        transition: transform 3s;
    }

    .back {
        transform-origin: 100% 0;
        transform: rotateY(180deg);
        left: 0;
    }

    .front {
        transform-origin: 0 0;
        transform: rotateY(0deg);
        right: 0;
    }

    .back.flipped {
        transform: rotateY(0deg);
    }

    .front.flipped {
        transform: rotateY(-180deg);
    }

    .clickable {
        pointer-events: all;
    }

    .cover,
    .lastpage {
        top: 0;
        bottom: 0;
        width: calc(50% + 0.5em);
        border-style: solid;
        border-image: linear-gradient(220.55deg, #FFD439 0%, #FF7A00 100%);
        border-image-slice: 1;
    }

    .front.cover {
        pointer-events: all;
        right: -0.5em;
        border: none;
        margin-left: -0.1em;
        padding: 0.5em 0.25em;
        color: #fff;
        background: linear-gradient(220.55deg, #FFD439 0%, #FF7A00 100%);
        box-shadow: inset 3em 0 hsl(0, 0%, 0%);
        border-radius: 0 5px 5px 0;
    }

    .back.cover {
        left: -0.5em;
        border-width: 0.5em 0 0.5em 0.5em;
        border-radius: 5px 0 0 5px;
    }

    .lastpage {
        right: -0.5em;
        border-width: 0.5em 0.5em 0.5em 0;
        border-radius: 0 5px 5px 0;
    }

    .bookpage .booktitle {
        padding: 3em 0.5em 0.5em 2em;
    }

    .bookpage footer {
        position: absolute;
        bottom: 0;
        margin: 4em 2em;
        font-size: 0.9em;
    }

    .bookpage:nth-child(n+3)::before {
        content: counter(pagecounter);
        display: block;
        padding: 1em 2em;
    }

    .bookpage:nth-child(odd)::before {
        text-align: right;
    }

    /* ************************** BOOK DESKTOP RTL ********************* */
    .bookmat.rtl {
        flex-direction: row-reverse;
    }

    .rtl .preface {
        text-align: right;
    }

    .rtl .book {
        transform: rotate(-20deg) scale(0.5);
    }

    .rtl .opened.book {
        transform: rotate(0);
    }

    .rtl .back {
        transform-origin: 0 0;
        transform: rotateY(-180deg);
        left: auto;
        right: 0;
    }

    .rtl .front {
        transform-origin: 100% 0;
        transform: rotateY(0deg);
        left: 0;
    }

    .rtl .back.flipped {
        transform: rotateY(0deg);
    }

    .rtl .front.flipped {
        transform: rotateY(180deg);
    }

    .rtl .front.cover {
        margin-right: -0.1em;
        border-radius: 5px 0 0 5px;
        box-shadow: inset -3em 0 hsl(0, 0%, 0%);
    }

    .rtl .lastpage {
        left: -0.5em;
        border-width: 0.5em 0 0.5em 0.5em;
        border-radius: 5px 0 0 5px;
    }

    .rtl .back.cover {
        left: auto;
        right: -0.5em;
        border-width: 0.5em 0.5em 0.5em 0;
        border-radius: 0 5px 5px 0;
    }

    .rtl .bookpage:nth-child(even)::before {
        text-align: right;
    }

    .rtl .bookpage:nth-child(odd)::before {
        text-align: left;
    }

    .rtl .bookpage .booktitle {
        padding: 3em 1.5em 0 0;
    }
}