.intro-screen{
    display: none;
    flex-direction: column;
    align-items: center;
    gap: 40px;
    position: fixed;
    inset: 0;
    overflow-y: auto;
    padding: 30px 20px;
    z-index: 3;
    scrollbar-color: #cfcfcf #00000f;
}

.intro-title{
    font-size: 5rem;
}

.intro-image{
    width: 400px;
    max-width: 90%;
    border: 1px solid rgb(0, 0, 36);
    box-shadow: 0 0 20px rgba(0, 0, 255, 1);
    -webkit-box-shadow: 0 0 20px rgba(0, 0, 255, 1);
    -moz-box-shadow: 0 0 20px rgba(0, 0, 255, 1);
}

.intro-text{
    display: flex;
    flex-direction: column;
    gap: 20px;
    width: 70vw;
    max-width: 900px;
}

.intro-text p{
    color: #cfcfcf;
    text-align: center;
    font-size: 2rem;
    text-shadow: 0 0 10px rgba(0, 0, 255, 1);
    -webkit-text-shadow: 0 0 10px rgba(0, 0, 255, 1);
    -moz-text-shadow: 0 0 10px rgba(0, 0, 255, 1);
}

.intro-buttons{
    display: flex;
    gap: 30px;
    margin-top: auto;
    padding-top: 20px;
}

.intro-buttons .button{
    min-width: 160px;
}

/* locked button (the Test button starts with the "disabled" attribute) */
.button:disabled,
.button:disabled:hover{
    background-color: #6e6e6e;
    color: #3a3a3a;
    cursor: not-allowed;
    box-shadow: none;
    border: 1px solid rgb(0, 0, 36);
}

.button:disabled::after{
    content: " (locked)";
}

.book-button{
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: #cfcfcf;
    position: fixed;
    top: 0;
    left: 0;
    margin: 15px;
    padding: 20px;
    width: 30px;
    height: 30px;
    z-index: 5;
}

.intro-back{
    position: fixed;
    top: 0;
    right: 0;
    margin: 15px;
    width: 120px;
    height: 50px;
    z-index: 5;
}

/* the book view: a dark blurry layer with the book on top */
.book-overlay{
    display: none;
    align-items: center;
    justify-content: center;
    position: fixed;
    inset: 0;
    z-index: 20;
    background-color: rgba(0, 0, 15, 0.6);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
}

.book{
    display: flex;
    width: 80vw;
    max-width: 1000px;
    height: 70vh;
    background-color: #b6b5b5;
    border: 1px solid rgb(0, 0, 36);
    box-shadow: 0 0 20px rgba(0, 0, 255, 1);
    -webkit-box-shadow: 0 0 20px rgba(0, 0, 255, 1);
    -moz-box-shadow: 0 0 20px rgba(0, 0, 255, 1);
}

.page{
    flex: 1;
    margin: 10px;
    padding: 30px;
    overflow-y: auto;
    background-color: #cfcfcf;
    color: #000024;
    font-size: 1.5rem;
}

.book-close{
    position: absolute;
    top: 0;
    right: 0;
    margin: 15px;
    width: 120px;
    height: 50px;
}