body{
    margin: 0;
    font-family: 'Poppins', sans-serif;
    background: linear-gradient(135deg, #0f2027, #203a43, #2c5364);
    height: 100vh;
}
.cover_page {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

/* BOOK CONTAINER */
.container {
    perspective: 2000px;
}

/* BOOK */
.book {
    width: 520px;
    height: 550px;
    position: relative;
    transform-style: preserve-3d;
}

/* COVERS */
.cover {
    width: 100%;
    height: 100%;
    position: absolute;
    background: #111;
    border-radius: 10px;
    box-shadow: 0 20px 40px rgba(0,0,0,0.6);
    transform-origin: left;
    transition: transform 1.5s ease;
}

/* LEFT SIDE */
.left {
    background: #222;
    z-index: 1;
}

/* RIGHT SIDE (FRONT COVER) */
.right {
    background: linear-gradient(145deg, #ff7e5f, #feb47b);
    display: flex;
    justify-content: center;
    align-items: center;
    transform-origin: left;
    z-index: 2;
}

/* CONTENT INSIDE */
.content {
    text-align: center;
    color: white;
    padding: 20px;
}

.logo {
    width: 200px;
    margin-bottom: 10px;
}

h1 {
    margin: 10px 0;
}

/* BUTTON */
button {
    padding: 12px 20px;
    border: none;
    background: #fff;
    color: #333;
    font-weight: bold;
    border-radius: 25px;
    cursor: pointer;
    transition: 0.3s;
}

button:hover {
    background: #000;
    color: #fff;
}

/* OPEN ANIMATION */
.book.open .right {
    transform: rotateY(-160deg);
}

.book.open .left {
    transform: rotateY(-10deg);
}