:root {
    --bg-primary: #0a1a0f;
    --bg-secondary: #1a2f1f;
    --bg-card: #243328;
    --text-primary: #e8f5e8;
    --text-secondary: #b8d4b8;
    --accent-green: #4ade80;
    --accent-dark: #16a34a;
    --error: #ef4444;
    --success: #22c55e;
    --warning: #f59e0b;
    --shadow: rgba(0, 0, 0, 0.3);
    --border: #3a5a3a;
}

[data-theme="light"] {
    --bg-primary: #f0f9f0;
    --bg-secondary: #e0f2e0;
    --bg-card: #ffffff;
    --text-primary: #0a2010;
    --text-secondary: #2a4a2a;
    --accent-green: #16a34a;
    --accent-dark: #065f46;
    --shadow: rgba(0, 0, 0, 0.1);
    --border: #a7c7a7;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, var(--bg-primary) 0%, var(--bg-secondary) 100%);
    color: var(--text-primary);
    min-height: 100vh;
    position: relative;
    overflow-x: hidden;
    transition: all 0.3s ease;
    display: flex;
    flex-direction: column;
}

.background-animation {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: 
        radial-gradient(circle at 20% 80%, rgba(74, 222, 128, 0.05) 0%, transparent 50%),
        radial-gradient(circle at 80% 20%, rgba(34, 197, 94, 0.05) 0%, transparent 50%);
    pointer-events: none;
    z-index: -1;
}

header {
    text-align: center;
    padding: 2rem;
    background: var(--bg-card);
    box-shadow: 0 4px 6px var(--shadow);
    position: relative;
}

h1 {
    font-size: 2.5rem;
    color: var(--accent-green);
    text-shadow: 2px 2px 4px var(--shadow);
    animation: float 3s ease-in-out infinite;
}

.subtitle {
    color: var(--text-secondary);
    margin-top: 0.5rem;
    font-size: 1.1rem;
}

.theme-btn {
    position: absolute;
    top: 2rem;
    right: 2rem;
    background: var(--accent-dark);
    border: none;
    border-radius: 50%;
    width: 50px;
    height: 50px;
    cursor: pointer;
    font-size: 1.5rem;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    box-shadow: 0 2px 8px var(--shadow);
}

.theme-btn:hover {
    transform: scale(1.1) rotate(20deg);
    box-shadow: 0 4px 12px var(--shadow);
}

main {
    flex: 1;
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 1rem;
    display: grid;
    grid-template-columns: 1fr 2fr 1fr;
    gap: 2rem;
    width: 100%;
}

.settings-panel, .problem-area, .stats-panel {
    background: var(--bg-card);
    border-radius: 15px;
    padding: 1.5rem;
    box-shadow: 0 8px 16px var(--shadow);
    border: 1px solid var(--border);
    transition: transform 0.3s ease;
}

.settings-panel:hover, .problem-area:hover, .stats-panel:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 20px var(--shadow);
}

h2, h3 {
    color: var(--accent-green);
    margin-bottom: 1rem;
}

.setting-group {
    margin-bottom: 1rem;
}

.setting-label {
    display: block;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

select, input[type="text"] {
    width: 100%;
    padding: 0.75rem;
    margin-top: 0.5rem;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    color: var(--text-primary);
    font-size: 1rem;
    transition: all 0.3s ease;
}

select:focus, input[type="text"]:focus {
    outline: none;
    border-color: var(--accent-green);
    box-shadow: 0 0 0 3px rgba(74, 222, 128, 0.1);
}

.checkbox-label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-secondary);
    cursor: pointer;
}

input[type="checkbox"] {
    width: 20px;
    height: 20px;
    accent-color: var(--accent-green);
}

.btn-primary, .btn-check, .btn-hint, .btn-secondary {
    width: 100%;
    padding: 0.75rem;
    margin-top: 1rem;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
}

.btn-primary {
    background: linear-gradient(135deg, var(--accent-green), var(--accent-dark));
    color: white;
}

.btn-check {
    background: var(--success);
    color: white;
}

.btn-hint {
    background: var(--warning);
    color: white;
}

.btn-secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
}

.btn-primary:hover, .btn-check:hover, .btn-hint:hover, .btn-secondary:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px var(--shadow);
}

.problem-display {
    text-align: center;
    margin-bottom: 2rem;
}

.expression {
    font-size: 2rem;
    font-family: 'Courier New', monospace;
    background: var(--bg-secondary);
    padding: 1.5rem;
    border-radius: 10px;
    border: 2px dashed var(--accent-green);
    margin-top: 1rem;
    min-height: 80px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.answer-section {
    margin-bottom: 1rem;
}

.answer-section label {
    display: block;
    margin-bottom: 0.5rem;
    color: var(--text-secondary);
}

.button-group {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

.feedback, .hint {
    padding: 1rem;
    border-radius: 8px;
    margin-top: 1rem;
    display: none;
    animation: slideIn 0.3s ease;
}

.feedback.show, .hint.show {
    display: block;
}

.feedback.success {
    background: rgba(34, 197, 94, 0.2);
    border: 1px solid var(--success);
    color: var(--success);
}

.feedback.error {
    background: rgba(239, 68, 68, 0.2);
    border: 1px solid var(--error);
    color: var(--error);
}

.hint {
    background: rgba(245, 158, 11, 0.2);
    border: 1px solid var(--warning);
    color: var(--warning);
}

.stats-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
    margin-bottom: 1rem;
}

.stat-item {
    background: var(--bg-secondary);
    padding: 0.75rem;
    border-radius: 8px;
    text-align: center;
}

.stat-label {
    display: block;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.stat-value {
    display: block;
    font-size: 1.5rem;
    font-weight: bold;
    margin-top: 0.25rem;
}

.stat-value.success {
    color: var(--success);
}

.stat-value.streak {
    color: var(--accent-green);
}

.leaves {
    position: fixed;
    top: -50px;
    width: 100%;
    pointer-events: none;
    z-index: 100;
}

.leaf {
    position: absolute;
    font-size: 2rem;
    animation: fall linear infinite;
    opacity: 0.7;
}

.leaf1 {
    left: 10%;
    animation-duration: 15s;
    animation-delay: 0s;
}

.leaf2 {
    left: 30%;
    animation-duration: 12s;
    animation-delay: 3s;
}

.leaf3 {
    left: 60%;
    animation-duration: 18s;
    animation-delay: 7s;
}

.leaf4 {
    left: 85%;
    animation-duration: 20s;
    animation-delay: 10s;
}

footer {
    background: var(--bg-card);
    border-top: 1px solid var(--border);
    padding: 2rem 1rem;
    margin-top: 2rem;
    box-shadow: 0 -4px 6px var(--shadow);
}

.footer-content {
    max-width: 1200px;
    margin: 0 auto;
    text-align: center;
}

.footer-content p {
    color: var(--text-secondary);
    margin-bottom: 1rem;
    font-size: 1rem;
}

.footer-links {
    display: flex;
    justify-content: center;
    gap: 2rem;
    flex-wrap: wrap;
}

.footer-links a {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--accent-green);
    text-decoration: none;
    font-weight: 500;
    transition: all 0.3s ease;
    padding: 0.5rem 1rem;
    border-radius: 8px;
}

.footer-links a:hover {
    color: var(--accent-dark);
    background: var(--bg-secondary);
    transform: translateY(-2px);
}

.footer-links svg {
    flex-shrink: 0;
}

@keyframes fall {
    0% {
        transform: translateY(0) rotate(0deg);
    }
    100% {
        transform: translateY(100vh) rotate(360deg);
    }
}

@keyframes float {
    0%, 100% {
        transform: translateY(0);
    }
    50% {
        transform: translateY(-10px);
    }
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@media (max-width: 768px) {
    main {
        grid-template-columns: 1fr;
    }
    
    h1 {
        font-size: 2rem;
    }
    
    .expression {
        font-size: 1.5rem;
    }
    
    .theme-btn {
        top: 1rem;
        right: 1rem;
    }

    .footer-links {
        flex-direction: column;
        gap: 1rem;
    }
}