* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
}

:root {
    --bg-color: #f7f9fa;
    --text-color: #1c1e21;
    --card-bg: #ffffff;
    --accent: #9ca3af;
    --accent-hover: #6b7280;
    --border-color: #e4e7eb;
    --success: #10b981;
    --success-bg: #d1fae5;
    --error: #ef4444;
    --error-bg: #fee2e2;
    
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
    --transition: 0.3s ease;
}

[data-theme="dark"] {
    --bg-color: #121212;
    --text-color: #ffffff;
    --card-bg: #1e1e1e;
    --accent: #555555;
    --accent-hover: #777777;
    --border-color: #333333;
    --success: #34d399;
    --success-bg: rgba(16, 185, 129, 0.2);
    --error: #f87171;
    --error-bg: rgba(239, 68, 68, 0.2);
    
    --shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    flex-direction: column;
    justify-content: center;
    min-height: 100vh;
    transition: background-color var(--transition), color var(--transition);
}

.app-header {
    position: absolute;
    top: 1rem;
    right: 1.5rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

#lang-toggle {
    font-weight: 600;
    font-size: 0.9rem;
}

.theme-toggle {
    background: transparent;
    border: none;
    color: var(--text-color);
    cursor: pointer;
    padding: 0.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: color var(--transition);
    border-radius: 50%;
}

.theme-toggle:hover {
    background: var(--border-color);
}

.hidden {
    display: none !important;
}

.app-main {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 2rem;
    max-width: 600px;
    margin: 0 auto;
    width: 100%;
}

.challenge-section {
    text-align: center;
    margin-bottom: 3rem;
    width: 100%;
}

.challenge-label {
    font-size: 0.9rem;
    color: var(--text-color);
    opacity: 0.7;
    margin-bottom: 1rem;
    text-transform: uppercase;
    letter-spacing: 1.5px;
}

.challenge-display {
    font-size: 4rem;
    font-weight: 700;
    line-height: 1.2;
    transition: transform 0.2s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    min-height: 120px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.options-section {
    width: 100%;
}

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

.option-btn {
    background-color: var(--card-bg);
    color: var(--text-color);
    border: 2px solid var(--border-color);
    border-radius: 16px;
    padding: 1rem;
    font-size: 1.2rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: var(--shadow);
}

.option-btn:hover {
    transform: translateY(-2px);
    border-color: var(--accent);
    box-shadow: 0 6px 16px rgba(0,0,0,0.1);
}

.option-btn:active {
    transform: translateY(0);
}

.option-btn.correct {
    background-color: var(--success-bg);
    border-color: var(--success);
    color: var(--success);
    animation: pulse-green 0.5s ease;
}

.option-btn.incorrect {
    background-color: var(--error-bg);
    border-color: var(--error);
    color: var(--error);
    animation: shake 0.4s cubic-bezier(.36,.07,.19,.97) both;
}

body.success-state {
    background-color: var(--success-bg);
}

@keyframes shake {
    10%, 90% { transform: translate3d(-1px, 0, 0); }
    20%, 80% { transform: translate3d(2px, 0, 0); }
    30%, 50%, 70% { transform: translate3d(-4px, 0, 0); }
    40%, 60% { transform: translate3d(4px, 0, 0); }
}

@keyframes pulse-green {
    0% { transform: scale(1); }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); }
}

@media (max-width: 480px) {
    .challenge-display {
        font-size: 3.5rem;
    }
    
    .option-btn {
        padding: 0.8rem 0.5rem;
        font-size: 1rem;
    }
}