/* App Container: 1000px x 900px TOTAL */
#brain-games-app {
    width: 1000px;
    height: 900px;
    max-width: 100%;
    margin: 0 auto;
    background: white;
    font-family: 'Segoe UI', Arial, sans-serif;
    position: relative;
}

/* Tabs: Yellow PLAY (500x60px) + Orange BOOK (500x60px) */
.tabs {
    display: flex;
    height: 60px;
}

.tab {
    width: 500px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.1rem;
    font-weight: 600;
    letter-spacing: 2px;
    cursor: pointer;
    transition: all 0.2s ease;
    opacity: 0.7;
}

.tab.active {
    opacity: 1;
}

.tab:hover {
    opacity: 1;
}

.tab-play {
    background: #f9e547;
    color: #333;
}

.tab-book {
    background: #f5a142;
    color: white;
}

/* App sections */
.app-section {
    display: none;
}

.app-section.active {
    display: block;
}

#book-section {
    height: 840px;
    overflow: hidden;
}

.credit {
    text-align: center;
    padding: 1rem;
    color: #666;
    font-size: 0.85rem;
    font-style: italic;
}

/* Intro Screen Overlay - Centered Panel Over Page */
#intro-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.3); /* Semi-transparent backdrop */
    z-index: 9999;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 1;
    visibility: visible;
    transition: opacity 0.5s ease, visibility 0.5s ease;
}

#intro-overlay.hidden {
    opacity: 0;
    visibility: hidden;
}

.intro-content {
    text-align: center;
    width: 950px;
    height: 830px;
    max-width: 95%;
    max-height: 95vh;
    padding: 50px 60px;
    background: linear-gradient(135deg, #5A8A8F 0%, #6B9EA3 100%);
    border-radius: 30px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.4);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

.intro-brain-image {
    width: 160px;
    height: 160px;
    margin: 0 auto 35px;
    background: white;
    border-radius: 50%;
    padding: 8px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
    overflow: hidden;
}

.intro-brain-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    border-radius: 50%;
}

.intro-title {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    font-size: 48px;
    font-weight: 700;
    color: #FFFFFF;
    margin: 0 0 25px 0;
    line-height: 1.2;
    letter-spacing: 1px;
    text-transform: uppercase;
}

.intro-description {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    font-size: 18px;
    font-weight: 400;
    color: #FFFFFF;
    line-height: 1.55;
    margin: 0 0 40px 0;
    max-width: 750px;
}

.intro-go-button {
    background: #E66B7A;
    color: white;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    font-size: 28px;
    font-weight: 700;
    padding: 12px 55px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 6px 18px rgba(230, 107, 122, 0.4);
    text-transform: uppercase;
    letter-spacing: 2px;
}

.intro-go-button:hover {
    background: #D85866;
    transform: translateY(-2px);
    box-shadow: 0 8px 24px rgba(230, 107, 122, 0.5);
}

.intro-go-button:active {
    transform: translateY(0px);
}

.intro-credit {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    font-size: 13px;
    font-style: italic;
    color: rgba(255, 255, 255, 0.85);
    margin-top: 35px;
}

/* Mobile Responsive for Intro Screen */
@media (max-width: 1000px) {
    .intro-content {
        width: 90%;
        height: auto;
        padding: 40px 30px;
    }
    
    .intro-brain-image {
        width: 130px;
        height: 130px;
        margin-bottom: 25px;
    }
    
    .intro-title {
        font-size: 36px;
    }
    
    .intro-description {
        font-size: 16px;
        margin-bottom: 30px;
    }
    
    .intro-go-button {
        font-size: 24px;
        padding: 10px 45px;
    }
    
    .intro-credit {
        font-size: 12px;
        margin-top: 25px;
    }
}

@media (max-width: 600px) {
    .intro-content {
        padding: 30px 25px;
    }
    
    .intro-brain-image {
        width: 110px;
        height: 110px;
    }
    
    .intro-title {
        font-size: 28px;
    }
    
    .intro-description {
        font-size: 14px;
    }
    
    .intro-go-button {
        font-size: 22px;
        padding: 10px 40px;
    }
}