:root {
    --bg-color: #f0f8ff;
    --primary-color: #4a90e2;
    --secondary-color: #50e3c2;
    --accent-color: #ffd700;
    --text-color: #333;
    --white: #fff;
    --success-color: #28a745;
    --error-color: #dc3545;
    --card-bg: #ffffff;
    --shadow: 0 4px 8px rgba(0,0,0,0.1);
}

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

body {
    font-family: 'Poppins', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 1rem;
}

main {
    width: 100%;
    max-width: 600px;
    text-align: center;
}

header {
    margin-bottom: 1.5rem;
}

h1 {
    color: var(--primary-color);
    font-size: clamp(1.8rem, 5vw, 2.5rem);
    margin-bottom: 0.5rem;
}

#instruction {
    font-size: clamp(1rem, 3vw, 1.2rem);
    color: #555;
}

#game-board {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    margin: 0 auto;
    width: 100%;
    max-width: 500px;
    aspect-ratio: 4 / 3;
}

.card {
    background-color: var(--card-bg);
    border-radius: 8px;
    box-shadow: var(--shadow);
    cursor: pointer;
    overflow: hidden;
    position: relative;
    transition: transform 0.2s ease-in-out, box-shadow 0.2s ease-in-out;
    aspect-ratio: 1 / 1;
    display: flex;
    justify-content: center;
    align-items: center;
}

.card:hover {
    transform: scale(1.05);
    box-shadow: 0 8px 16px rgba(0,0,0,0.2);
}

.card.selected {
    outline: 4px solid var(--accent-color);
    transform: scale(1.02);
}

.card.correct {
    outline: 4px solid var(--success-color);
}

.card.incorrect {
    outline: 4px solid var(--error-color);
    animation: shake 0.5s;
}

.card img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
}

#feedback-container {
    margin-top: 1.5rem;
    height: 60px; /* Reserve space to prevent layout shifts */
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

#feedback-message {
    font-size: 1.2rem;
    font-weight: 600;
    min-height: 28px;
}

#next-level-btn {
    background-color: var(--primary-color);
    color: var(--white);
    border: none;
    border-radius: 8px;
    padding: 12px 24px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.2s, transform 0.2s;
    margin-top: 10px;
    box-shadow: var(--shadow);
}

#next-level-btn:hover {
    background-color: #357abd;
    transform: translateY(-2px);
}

.hidden {
    display: none;
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

/* Modal Styles */
.modal {
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0,0,0,0.5);
    display: flex;
    justify-content: center;
    align-items: center;
}

.modal.hidden {
    display: none;
}

.modal-content {
    background-color: var(--white);
    padding: 30px;
    border-radius: 12px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.2);
    text-align: center;
    width: 80%;
    max-width: 350px;
    animation: zoomIn 0.3s ease-out;
}

.modal-content h2 {
    color: var(--success-color);
    font-size: clamp(2rem, 8vw, 2.5rem);
    margin-bottom: 20px;
}

#modal-next-btn {
    background-color: var(--primary-color);
    color: var(--white);
    border: none;
    border-radius: 8px;
    padding: 12px 24px;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.2s, transform 0.2s;
    box-shadow: var(--shadow);
}

#modal-next-btn:hover {
    background-color: #357abd;
    transform: translateY(-2px);
}

@keyframes zoomIn {
    from {
        opacity: 0;
        transform: scale(0.8);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}