:root {
    /* Color Palette */
    --primary-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --secondary-gradient: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    --success-gradient: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    --error-gradient: linear-gradient(135deg, #fa709a 0%, #fee140 100%);

    --bg-dark: #0f0c29;
    --bg-mid: #1a1640;
    --bg-light: #24204d;

    --text-primary: #ffffff;
    --text-secondary: #b8b5d1;
    --text-muted: #7c7a92;

    --glass-bg: rgba(255, 255, 255, 0.15);
    --glass-border: rgba(255, 255, 255, 0.25);

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;

    /* Border Radius */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;

    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.2);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.3);
    --shadow-glow: 0 0 20px rgba(102, 126, 234, 0.5);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: var(--bg-dark);
    color: var(--text-primary);
    min-height: 100vh;
    overflow-x: hidden;
    position: relative;
}

.background-gradient {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(rgba(15, 12, 41, 0.7), rgba(15, 12, 41, 0.7)), url('background.png');
    background-size: cover;
    background-position: center;
    background-attachment: fixed;
    z-index: -1;
}

@keyframes rotate {
    from {
        transform: rotate(0deg);
    }

    to {
        transform: rotate(360deg);
    }
}

.container {
    max-width: 600px;
    margin: 0 auto;
    padding: var(--spacing-lg);
    position: relative;
    z-index: 1;
}

/* Header */
.header {
    text-align: center;
    margin-bottom: var(--spacing-md);
    animation: fadeInDown 0.6s ease-out;
}

.title {
    font-family: 'Orbitron', sans-serif;
    font-size: 2rem;
    font-weight: 900;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-xs);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
}

.title-icon {
    font-size: 1.5rem;
    filter: drop-shadow(0 0 10px rgba(102, 126, 234, 0.8));
}

.subtitle {
    color: var(--text-secondary);
    font-size: 1rem;
    font-weight: 500;
}

/* Screen Visibility */
.hidden {
    display: none !important;
}

/* Title Screen */
.title-screen {
    min-height: 80vh;
    display: flex;
    align-items: center;
    justify-content: center;
    animation: fadeIn 0.8s ease-out;
}

.title-screen-content {
    text-align: center;
    max-width: 500px;
}

.main-title {
    font-family: 'Orbitron', sans-serif;
    font-size: 3rem;
    font-weight: 900;
    margin-bottom: var(--spacing-md);
    animation: fadeInDown 0.6s ease-out;
}

.title-icon-large {
    font-size: 3.5rem;
    display: block;
    margin-bottom: var(--spacing-sm);
    filter: drop-shadow(0 0 20px rgba(102, 126, 234, 0.8));
    animation: float 3s ease-in-out infinite;
}

.title-text {
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    display: block;
}

.main-subtitle {
    color: var(--text-secondary);
    font-size: 1.125rem;
    font-weight: 500;
    margin-bottom: var(--spacing-xl);
    animation: fadeIn 0.6s ease-out 0.2s both;
}

.difficulty-section {
    animation: fadeIn 0.6s ease-out 0.4s both;
}

.difficulty-title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-lg);
}

.digit-selection {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--spacing-sm);
    margin-top: var(--spacing-lg);
}

.digit-btn {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 2px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md) var(--spacing-sm);
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-md);
    position: relative;
    overflow: hidden;
}

.digit-btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--primary-gradient);
    opacity: 0;
    transition: opacity 0.3s ease;
    z-index: -1;
}

.digit-btn:hover::before {
    opacity: 1;
}

.digit-btn:hover {
    transform: translateY(-4px);
    border-color: rgba(102, 126, 234, 0.8);
    box-shadow: var(--shadow-lg), var(--shadow-glow);
}

.digit-btn:active {
    transform: translateY(-2px);
}

.digit-number {
    font-family: 'Orbitron', sans-serif;
    font-size: 2.5rem;
    font-weight: 900;
    color: var(--text-primary);
    display: block;
    margin-bottom: var(--spacing-xs);
    position: relative;
    z-index: 1;
}

.digit-label {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-secondary);
    display: block;
    position: relative;
    z-index: 1;
}

.digit-btn:hover .digit-number,
.digit-btn:hover .digit-label {
    color: white;
}

/* How to Play Button */
.how-to-play-btn {
    width: 100%;
    margin-top: var(--spacing-lg);
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 2px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md);
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-md);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    position: relative;
    overflow: hidden;
}

.how-to-play-btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    opacity: 0;
    transition: opacity 0.3s ease;
    z-index: -1;
}

.how-to-play-btn:hover::before {
    opacity: 1;
}

.how-to-play-btn:hover {
    transform: translateY(-4px);
    border-color: rgba(79, 172, 254, 0.8);
    box-shadow: var(--shadow-lg), 0 0 20px rgba(79, 172, 254, 0.5);
}

.how-to-play-btn:active {
    transform: translateY(-2px);
}

.how-to-play-icon {
    font-size: 1.5rem;
    position: relative;
    z-index: 1;
}

.how-to-play-text {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    position: relative;
    z-index: 1;
}

.how-to-play-btn:hover .how-to-play-text {
    color: white;
}

/* Game Header Actions */
.game-header-actions {
    display: flex;
    justify-content: flex-start;
    margin-bottom: var(--spacing-xs);
    animation: fadeIn 0.6s ease-out 0.1s both;
}

.game-back-btn {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-md);
    padding: var(--spacing-xs) var(--spacing-sm);
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.game-back-btn:hover {
    background: rgba(255, 255, 255, 0.2);
    color: var(--text-primary);
    transform: translateX(-2px);
    border-color: var(--glass-border);
}

/* Game Screen */
.game-screen {
    animation: fadeIn 0.6s ease-out;
}


/* Game Container */
.game-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

/* Score Panel */
.score-panel {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md);
    display: flex;
    justify-content: space-around;
    align-items: center;
    box-shadow: var(--shadow-md);
    animation: fadeIn 0.6s ease-out 0.2s both;
}

.score-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
}

.score-label {
    font-size: 0.875rem;
    color: var(--text-muted);
    font-weight: 500;
}

.score-value {
    font-family: 'Orbitron', sans-serif;
    font-size: 1.5rem;
    font-weight: 700;
    background: var(--success-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.score-divider {
    width: 1px;
    height: 40px;
    background: var(--glass-border);
}

/* Pyramid Container */
.pyramid-container {
    animation: fadeIn 0.6s ease-out 0.3s both;
}

.pyramid-card {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
}

.pyramid-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    text-align: center;
    color: var(--text-secondary);
}

.pyramid {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-sm);
}

.pyramid-row {
    display: flex;
    gap: var(--spacing-sm);
    animation: slideIn 0.4s ease-out backwards;
}

.pyramid-number {
    min-width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--primary-gradient);
    border-radius: var(--radius-sm);
    font-family: 'Orbitron', sans-serif;
    font-size: 1.5rem;
    font-weight: 700;
    color: white;
    box-shadow: var(--shadow-sm);
    transition: transform 0.2s ease;
}

.pyramid-number:hover {
    transform: scale(1.05);
}

.pyramid-number.result {
    background: linear-gradient(135deg, #f5af19 0%, #f12711 100%);
    box-shadow: 0 0 20px rgba(245, 175, 25, 0.6), var(--shadow-md);
    animation: pulseGlow 1.5s ease-in-out infinite;
}

@keyframes pulseGlow {

    0%,
    100% {
        box-shadow: 0 0 20px rgba(245, 175, 25, 0.6), var(--shadow-md);
    }

    50% {
        box-shadow: 0 0 30px rgba(245, 175, 25, 0.9), var(--shadow-lg);
    }
}

/* Answer Section */
.answer-section {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
    animation: fadeIn 0.6s ease-out 0.4s both;
}

.answer-display-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.answer-label {
    font-size: 0.875rem;
    color: var(--text-muted);
    font-weight: 500;
}

.answer-display {
    width: 100%;
    padding: var(--spacing-sm);
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 2px solid var(--glass-border);
    border-radius: var(--radius-md);
    font-family: 'Orbitron', sans-serif;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    text-align: center;
    box-shadow: var(--shadow-sm);
    transition: all 0.3s ease;
}

.answer-display:focus {
    outline: none;
    border-color: rgba(102, 126, 234, 0.8);
    box-shadow: var(--shadow-glow);
}

/* Calculator */
.calculator {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md);
    box-shadow: var(--shadow-md);
}

.calculator-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-sm);
}

.calc-btn {
    height: 50px;
    border: none;
    border-radius: var(--radius-md);
    font-family: 'Orbitron', sans-serif;
    font-size: 1.25rem;
    font-weight: 700;
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: var(--shadow-sm);
}

.number-btn {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
}

.number-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

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

.zero-btn {
    grid-column: span 1;
}

.clear-btn {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    color: white;
}

.clear-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.backspace-btn {
    background: linear-gradient(135deg, #ffecd2 0%, #fcb69f 100%);
    color: #333;
}

.backspace-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

/* Submit Button */
.submit-btn {
    width: 100%;
    padding: var(--spacing-sm);
    background: var(--success-gradient);
    border: none;
    border-radius: var(--radius-md);
    font-family: 'Inter', sans-serif;
    font-size: 1.125rem;
    font-weight: 700;
    color: white;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    box-shadow: var(--shadow-md);
    transition: all 0.3s ease;
}

.submit-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

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

.submit-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
}

/* Feedback Message */
.feedback-message {
    opacity: 0;
    transform: translateY(-10px);
    transition: all 0.3s ease;
    pointer-events: none;
}

.feedback-message.show {
    opacity: 1;
    transform: translateY(0);
}

.feedback-content {
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    font-size: 1.125rem;
    font-weight: 600;
    box-shadow: var(--shadow-md);
}

.feedback-message.correct .feedback-content {
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    color: white;
}

.feedback-message.incorrect .feedback-content {
    background: linear-gradient(135deg, #fa709a 0%, #fee140 100%);
    color: white;
}

.feedback-icon {
    font-size: 1.5rem;
}

/* Footer */
.footer {
    text-align: center;
    margin-top: var(--spacing-xl);
    padding-top: var(--spacing-lg);
    color: var(--text-muted);
    font-size: 0.875rem;
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }

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

@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }

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

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-20px);
    }

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

@keyframes float {

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

    50% {
        transform: translateY(-10px);
    }
}

/* How to Play Screen */
.how-to-play-screen {
    min-height: 100vh;
    padding: var(--spacing-lg) 0;
    animation: fadeIn 0.6s ease-out;
}

.how-to-play-content {
    max-width: 700px;
    margin: 0 auto;
}

.how-to-play-title {
    font-family: 'Orbitron', sans-serif;
    font-size: 2rem;
    font-weight: 900;
    margin-bottom: var(--spacing-xl);
    text-align: center;
    animation: fadeInDown 0.6s ease-out;
}

.how-to-play-title .title-icon-large {
    font-size: 2.5rem;
    display: block;
    margin-bottom: var(--spacing-sm);
    filter: drop-shadow(0 0 20px rgba(79, 172, 254, 0.8));
    animation: float 3s ease-in-out infinite;
}

.how-to-play-title .title-text {
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    display: block;
}

.how-to-play-sections {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-xl);
}

.how-to-play-card {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
    animation: fadeIn 0.6s ease-out backwards;
}

.how-to-play-card:nth-child(1) {
    animation-delay: 0.1s;
}

.how-to-play-card:nth-child(2) {
    animation-delay: 0.2s;
}

.how-to-play-card:nth-child(3) {
    animation-delay: 0.3s;
}

.how-to-play-card:nth-child(4) {
    animation-delay: 0.4s;
}

.how-to-play-section-title {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.how-to-play-text {
    color: var(--text-secondary);
    font-size: 1rem;
    line-height: 1.6;
    margin-bottom: var(--spacing-sm);
}

.how-to-play-text:last-child {
    margin-bottom: 0;
}

.how-to-play-text strong {
    color: var(--text-primary);
}

.highlight-answer {
    background: linear-gradient(135deg, #f5af19 0%, #f12711 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    font-size: 1.125rem;
}

/* Example Pyramid */
.example-pyramid {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-sm);
    margin: var(--spacing-md) 0;
    padding: var(--spacing-md);
    background: rgba(0, 0, 0, 0.2);
    border-radius: var(--radius-md);
}

.example-row {
    display: flex;
    gap: var(--spacing-sm);
}

.example-number {
    min-width: 45px;
    height: 45px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--primary-gradient);
    border-radius: var(--radius-sm);
    font-family: 'Orbitron', sans-serif;
    font-size: 1.25rem;
    font-weight: 700;
    color: white;
    box-shadow: var(--shadow-sm);
}

.example-number.result-example {
    background: linear-gradient(135deg, #f5af19 0%, #f12711 100%);
    box-shadow: 0 0 15px rgba(245, 175, 25, 0.6), var(--shadow-md);
}

/* How to Play Lists */
.how-to-play-list {
    color: var(--text-secondary);
    font-size: 1rem;
    line-height: 1.8;
    margin-left: var(--spacing-lg);
}

.how-to-play-list li {
    margin-bottom: var(--spacing-xs);
}

.how-to-play-list li:last-child {
    margin-bottom: 0;
}

.how-to-play-list strong {
    color: var(--text-primary);
}

/* Back to Title Button */
.back-to-title-btn {
    width: 100%;
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 2px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md);
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-md);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    position: relative;
    overflow: hidden;
    animation: fadeIn 0.6s ease-out 0.5s backwards;
}

.back-to-title-btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--primary-gradient);
    opacity: 0;
    transition: opacity 0.3s ease;
    z-index: -1;
}

.back-to-title-btn:hover::before {
    opacity: 1;
}

.back-to-title-btn:hover {
    transform: translateY(-4px);
    border-color: rgba(102, 126, 234, 0.8);
    box-shadow: var(--shadow-lg), var(--shadow-glow);
}

.back-to-title-btn:active {
    transform: translateY(-2px);
}

.back-btn-icon {
    font-size: 1.5rem;
    position: relative;
    z-index: 1;
}

.back-btn-text {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    position: relative;
    z-index: 1;
}

.back-to-title-btn:hover .back-btn-text {
    color: white;
}

/* Responsive Design */
@media (max-width: 640px) {
    .container {
        padding: var(--spacing-md);
    }

    .title {
        font-size: 2rem;
    }

    .subtitle {
        font-size: 0.875rem;
    }

    /* Digit Selection - Mobile Layout */
    .digit-selection {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-sm);
    }

    .digit-btn {
        padding: var(--spacing-sm);
    }

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

    .digit-label {
        font-size: 0.875rem;
    }

    .pyramid-number {
        min-width: 40px;
        height: 40px;
        font-size: 1.25rem;
    }

    .answer-display {
        font-size: 1.5rem;
    }

    .calc-btn {
        height: 45px;
        font-size: 1.125rem;
    }
}