:root {
    --primary-color: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --secondary-color: #ec4899;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    --bg-dark: #0f172a;
    --bg-darker: #020617;
    --card-bg: rgba(30, 41, 59, 0.8);
    --card-border: rgba(148, 163, 184, 0.1);
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --text-muted: #94a3b8;
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 20px rgba(99, 102, 241, 0.3);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'Helvetica Neue', Helvetica, Arial, sans-serif;
    background: linear-gradient(135deg, #0f172a 0%, #1e293b 50%, #0f172a 100%);
    color: var(--text-primary);
    min-height: 100vh;
    overflow-x: hidden;
    position: relative;
}

/* Animated Stars Background */
.stars-background {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 0;
    background-image:
        radial-gradient(2px 2px at 20px 30px, #eee, transparent),
        radial-gradient(2px 2px at 60px 70px, #fff, transparent),
        radial-gradient(1px 1px at 50px 50px, #ddd, transparent),
        radial-gradient(1px 1px at 130px 80px, #fff, transparent),
        radial-gradient(2px 2px at 90px 10px, #eee, transparent);
    background-size: 200px 200px;
    animation: stars 20s linear infinite;
    opacity: 0.3;
}

@keyframes stars {
    from {
        transform: translateY(0);
    }

    to {
        transform: translateY(-200px);
    }
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 2rem;
    position: relative;
    z-index: 1;
}

/* Header */
.game-header {
    text-align: center;
    margin-bottom: 3rem;
    animation: fadeInDown 0.8s ease-out;
}

.game-title {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1rem;
    margin-bottom: 0.5rem;
}

.title-number {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    font-size: 5rem;
    font-weight: 900;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    text-shadow: 0 0 30px rgba(99, 102, 241, 0.5);
    animation: pulse 2s ease-in-out infinite;
}

.title-text {
    font-size: 3rem;
    font-weight: 800;
    color: var(--text-primary);
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.5);
}

.game-subtitle {
    font-size: 1.1rem;
    color: var(--text-secondary);
    font-weight: 500;
}

/* Stats */
.game-stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 1rem;
    margin-bottom: 2rem;
    animation: fadeInUp 0.8s ease-out 0.2s backwards;
}

.stat-card {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--card-border);
    border-radius: 16px;
    padding: 1.5rem;
    display: flex;
    align-items: center;
    gap: 1rem;
    box-shadow: var(--shadow-md);
    transition: all 0.3s ease;
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg), var(--shadow-glow);
    border-color: var(--primary-color);
}

.stat-icon {
    font-size: 2.5rem;
    filter: drop-shadow(0 2px 4px rgba(0, 0, 0, 0.3));
}

.stat-label {
    font-size: 0.875rem;
    color: var(--text-muted);
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.stat-value {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-primary);
    font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
}

/* Game Board */
.game-board {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--card-border);
    border-radius: 24px;
    padding: 2.5rem;
    box-shadow: var(--shadow-lg);
    animation: fadeInUp 0.8s ease-out 0.4s backwards;
}

/* Numbers */
.numbers-container {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1rem;
    margin-bottom: 2rem;
}

.number-card {
    aspect-ratio: 1;
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 3rem;
    font-weight: 800;
    font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
    color: white;
    cursor: pointer;
    box-shadow: var(--shadow-md);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.number-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, transparent, rgba(255, 255, 255, 0.2));
    opacity: 0;
    transition: opacity 0.3s ease;
}

.number-card:hover::before {
    opacity: 1;
}

.number-card:hover {
    transform: translateY(-8px) scale(1.05);
    box-shadow: var(--shadow-lg), 0 0 30px rgba(99, 102, 241, 0.6);
}

.number-card:active {
    transform: translateY(-4px) scale(1.02);
}

.number-card.used {
    background: linear-gradient(135deg, #475569, #334155);
    opacity: 0.5;
    cursor: not-allowed;
    transform: scale(0.95);
}

.number-card.used:hover {
    transform: scale(0.95);
    box-shadow: var(--shadow-md);
}

.number-card.selected {
    background: linear-gradient(135deg, var(--secondary-color), #db2777);
    animation: selectedPulse 0.6s ease;
}

@keyframes selectedPulse {

    0%,
    100% {
        transform: scale(1);
    }

    50% {
        transform: scale(1.1);
    }
}

/* Expression Display */
.expression-display {
    background: rgba(15, 23, 42, 0.6);
    border: 2px solid var(--card-border);
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 2rem;
    min-height: 100px;
}

.expression-label {
    font-size: 0.875rem;
    color: var(--text-muted);
    margin-bottom: 0.5rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.expression-value {
    font-size: 1.5rem;
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    color: var(--text-primary);
    font-weight: 600;
    word-wrap: break-word;
    min-height: 2rem;
}

.expression-result {
    margin-top: 0.75rem;
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary-light);
}

/* Operators */
.operators-container {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 0.75rem;
    margin-bottom: 2rem;
}

.operator-btn {
    aspect-ratio: 1;
    background: linear-gradient(135deg, #1e293b, #334155);
    border: 2px solid var(--card-border);
    border-radius: 12px;
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--text-primary);
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-sm);
}

.operator-btn:hover {
    background: linear-gradient(135deg, #334155, #475569);
    border-color: var(--primary-color);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

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

.operator-btn.parenthesis {
    background: linear-gradient(135deg, #422006, #713f12);
    border-color: var(--warning-color);
}

.operator-btn.parenthesis:hover {
    background: linear-gradient(135deg, #713f12, #92400e);
}

/* Action Buttons */
.action-buttons {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1rem;
    margin-bottom: 2rem;
}

.action-btn {
    padding: 1rem 1.5rem;
    border: none;
    border-radius: 12px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-md);
    font-family: inherit;
}

.btn-icon {
    font-size: 1.25rem;
}

.clear-btn {
    background: linear-gradient(135deg, #475569, #64748b);
    color: white;
}

.clear-btn:hover {
    background: linear-gradient(135deg, #64748b, #94a3b8);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.submit-btn {
    background: linear-gradient(135deg, var(--success-color), #059669);
    color: white;
}

.submit-btn:hover {
    background: linear-gradient(135deg, #059669, #047857);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg), 0 0 20px rgba(16, 185, 129, 0.4);
}

.skip-btn {
    background: linear-gradient(135deg, var(--warning-color), #d97706);
    color: white;
}

.skip-btn:hover {
    background: linear-gradient(135deg, #d97706, #b45309);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

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

/* Hint Section */
.hint-section {
    text-align: center;
}

.hint-btn {
    background: linear-gradient(135deg, #7c3aed, #6d28d9);
    color: white;
    border: none;
    border-radius: 12px;
    padding: 0.875rem 2rem;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-md);
    font-family: inherit;
}

.hint-btn:hover {
    background: linear-gradient(135deg, #6d28d9, #5b21b6);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg), 0 0 20px rgba(124, 58, 237, 0.4);
}

.hint-icon {
    font-size: 1.25rem;
}

.hint-display {
    margin-top: 1rem;
    padding: 1rem;
    background: rgba(124, 58, 237, 0.1);
    border: 1px solid rgba(124, 58, 237, 0.3);
    border-radius: 8px;
    color: var(--text-secondary);
    font-weight: 500;
    min-height: 0;
    transition: all 0.3s ease;
}

.hint-display:empty {
    display: none;
}

/* Difficulty Selector */
.difficulty-selector {
    margin-top: 2rem;
    text-align: center;
    animation: fadeInUp 0.8s ease-out 0.6s backwards;
}

.difficulty-label {
    font-size: 1rem;
    color: var(--text-secondary);
    margin-bottom: 1rem;
    font-weight: 600;
}

.difficulty-buttons {
    display: inline-flex;
    gap: 0.75rem;
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    padding: 0.5rem;
    border-radius: 12px;
    border: 1px solid var(--card-border);
}

.difficulty-btn {
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: 8px;
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    background: transparent;
    color: var(--text-secondary);
    transition: all 0.3s ease;
    font-family: inherit;
}

.difficulty-btn:hover {
    color: var(--text-primary);
    background: rgba(99, 102, 241, 0.1);
}

.difficulty-btn.active {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: white;
    box-shadow: var(--shadow-sm);
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.8);
    backdrop-filter: blur(8px);
    z-index: 1000;
    align-items: center;
    justify-content: center;
    animation: fadeIn 0.3s ease;
}

.modal.show {
    display: flex;
}

.modal-content {
    background: linear-gradient(135deg, var(--bg-dark), #1e293b);
    backdrop-filter: blur(20px);
    border: 2px solid var(--card-border);
    border-radius: 24px;
    padding: 3rem;
    max-width: 450px;
    width: 90%;
    text-align: center;
    box-shadow: var(--shadow-lg), 0 0 60px rgba(0, 0, 0, 0.5);
    animation: modalSlideIn 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
    position: relative;
    overflow: hidden;
}

.modal-content.success {
    border-color: var(--success-color);
    box-shadow: 0 0 40px rgba(16, 185, 129, 0.2);
}

.modal-content.error {
    border-color: var(--danger-color);
    box-shadow: 0 0 40px rgba(239, 68, 68, 0.2);
}

.modal-content.warning {
    border-color: var(--warning-color);
    box-shadow: 0 0 40px rgba(245, 158, 11, 0.2);
}


.modal-icon {
    font-size: 5rem;
    margin-bottom: 1.5rem;
    animation: bounce 0.6s ease;
}

.modal-title {
    font-size: 2rem;
    font-weight: 800;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.modal-message {
    font-size: 1.125rem;
    color: var(--text-secondary);
    margin-bottom: 2rem;
    line-height: 1.6;
    white-space: pre-line;
}

.modal-btn {
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: 12px;
    padding: 1rem 2.5rem;
    font-size: 1.125rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-md);
    font-family: inherit;
    width: 100%;
}

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

.error .modal-btn {
    background: var(--danger-color);
}

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

.info .modal-btn {
    background: var(--primary-color);
}

.modal-btn:hover {
    filter: brightness(1.1);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

/* Particles */
.particles {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 999;
}

.particle {
    position: absolute;
    width: 10px;
    height: 10px;
    background: var(--primary-color);
    border-radius: 50%;
    animation: particleFloat 1s ease-out forwards;
    box-shadow: 0 0 10px var(--primary-color);
}

@keyframes particleFloat {
    0% {
        opacity: 1;
        transform: translateY(0) scale(1);
    }

    100% {
        opacity: 0;
        transform: translateY(-100px) scale(0);
    }
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-30px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes modalSlideIn {
    from {
        opacity: 0;
        transform: scale(0.9) translateY(20px);
    }

    to {
        opacity: 1;
        transform: scale(1) translateY(0);
    }
}

@keyframes pulse {

    0%,
    100% {
        opacity: 1;
    }

    50% {
        opacity: 0.8;
    }
}

@keyframes bounce {

    0%,
    100% {
        transform: translateY(0);
    }

    25% {
        transform: translateY(-20px);
    }

    50% {
        transform: translateY(0);
    }

    75% {
        transform: translateY(-10px);
    }
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 1rem;
    }

    .title-number {
        font-size: 3.5rem;
    }

    .title-text {
        font-size: 2rem;
    }

    .game-subtitle {
        font-size: 0.95rem;
    }

    .game-board {
        padding: 1.5rem;
    }

    .number-card {
        font-size: 2rem;
    }

    .operators-container {
        grid-template-columns: repeat(3, 1fr);
    }

    .action-buttons {
        grid-template-columns: 1fr;
    }

    .difficulty-buttons {
        flex-direction: column;
        width: 100%;
    }

    .difficulty-btn {
        width: 100%;
    }

    .modal-content {
        margin: 1rem;
        padding: 2rem;
    }
}

@media (max-width: 480px) {
    .numbers-container {
        grid-template-columns: repeat(2, 1fr);
    }

    .stat-value {
        font-size: 1.5rem;
    }

    .expression-value {
        font-size: 1.125rem;
    }
}