:root {
    --bg-color: #121212;
    --primary-color: #1e1e1e;
    --accent-color: #00ff7f;
    --text-color: #e0e0e0;
    --secondary-text-color: #a0a0a0;
    --border-color: #444;
    --correct-color: #28a745;
    --incorrect-color: #dc3545;
    --shadow-color: rgba(0, 255, 127, 0.1);
}

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

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

.container {
    background-color: var(--primary-color);
    padding: 2.5rem;
    border-radius: 15px;
    box-shadow: 0 8px 25px var(--shadow-color);
    text-align: center;
    width: 100%;
    max-width: 600px;
    border: 1px solid var(--border-color);
}

.screen {
    display: flex;
    flex-direction: column;
    align-items: center;
}

h1, h2 {
    color: var(--accent-color);
    margin-bottom: 1rem;
}

p {
    color: var(--secondary-text-color);
    margin-bottom: 2rem;
}

#difficulty-selection {
    display: flex;
    gap: 1rem;
}

.btn-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 1rem;
    width: 100%;
    margin-top: 1.5rem;
}

button {
    background-color: var(--accent-color);
    color: var(--bg-color);
    border: none;
    padding: 14px 22px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 1.1rem;
    font-weight: 600;
    transition: transform 0.2s, box-shadow 0.2s, background-color 0.2s;
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 15px rgba(0, 255, 127, 0.2);
}

.answer-btn {
    background-color: var(--primary-color);
    color: var(--text-color);
    border: 1px solid var(--border-color);
}

.answer-btn.correct {
    background-color: var(--correct-color);
    border-color: var(--correct-color);
    color: #fff;
}

.answer-btn.incorrect {
    background-color: var(--incorrect-color);
    border-color: var(--incorrect-color);
    color: #fff;
}

.feedback {
    margin-top: 1rem;
    font-weight: bold;
    min-height: 24px;
}

#next-btn, #restart-btn {
    margin-top: 1.5rem;
}

/* Custom Alert Styles */
.alert-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.7);
    display: none; /* Controlled by JS */
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.alert-box {
    background-color: var(--primary-color);
    padding: 2rem;
    border-radius: 15px;
    border: 1px solid var(--border-color);
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.5);
    text-align: center;
    width: 90%;
    max-width: 380px;
}

.alert-box h2 {
    color: var(--accent-color);
    margin-bottom: 1rem;
}

#alert-ok-btn {
    background-color: var(--accent-color);
    color: var(--bg-color);
    padding: 12px 30px;
    font-size: 1rem;
}

#alert-ok-btn:hover {
    box-shadow: 0 4px 12px rgba(0, 255, 127, 0.2);
}