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

:root {
    --primary-orange: #FF9500;
    --secondary-orange: #FF7500;
    --light-bg: #FFFFFF;
    --light-secondary-bg: #F5F5F7;
    --light-tertiary-bg: #EFEFEF;
    --light-text: #1C1C1E;
    --light-text-secondary: #6C6C70;
    --dark-bg: #0A0A0A;
    --dark-secondary-bg: #1C1C1E;
    --dark-tertiary-bg: #2C2C2E;
    --dark-text: #FFFFFF;
    --dark-text-secondary: #A1A1A6;
    --button-light: #E8E8ED;
    --button-dark: #2C2C2E;
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.08);
    --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.12);
    --shadow-lg: 0 16px 40px rgba(0, 0, 0, 0.16);
    --radius: 24px;
    --radius-sm: 12px;
    --transition: all 0.3s cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

html, body {
    height: 100%;
    width: 100%;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Helvetica Neue', sans-serif;
    background: var(--light-bg);
    color: var(--light-text);
    transition: var(--transition);
}

body.dark-mode {
    background: var(--dark-bg);
    color: var(--dark-text);
}

.wrapper {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* Header Styles */
.header {
    background: var(--light-secondary-bg);
    border-bottom: 1px solid var(--light-tertiary-bg);
    padding: 16px 0;
    transition: var(--transition);
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 100;
}

.dark-mode .header {
    background: var(--dark-secondary-bg);
    border-bottom-color: var(--dark-tertiary-bg);
}

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 24px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 28px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-orange), var(--secondary-orange));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.5px;
}

.header-controls {
    display: flex;
    gap: 20px;
    align-items: center;
}

.history-btn {
    display: flex;
    align-items: center;
    gap: 8px;
    background: var(--primary-orange);
    color: white;
    border: none;
    padding: 10px 18px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-weight: 600;
    font-size: 14px;
    transition: var(--transition);
    box-shadow: var(--shadow-sm);
}

.history-btn:hover {
    background: var(--secondary-orange);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

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

.history-btn .icon {
    font-size: 16px;
}

.theme-selector {
    display: flex;
    gap: 8px;
    background: var(--light-tertiary-bg);
    padding: 6px;
    border-radius: 10px;
    transition: var(--transition);
}

.dark-mode .theme-selector {
    background: var(--dark-tertiary-bg);
}

.theme-btn {
    width: 36px;
    height: 36px;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    font-size: 18px;
    transition: var(--transition);
    background: transparent;
    display: flex;
    align-items: center;
    justify-content: center;
}

.theme-btn.active {
    background: var(--light-bg);
    box-shadow: var(--shadow-sm);
}

.dark-mode .theme-btn.active {
    background: var(--dark-secondary-bg);
}

.theme-btn:hover {
    transform: scale(1.05);
}

/* Main Container */
.main-container {
    flex: 1;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 40px 20px;
    transition: var(--transition);
}

.calculator-wrapper {
    width: 100%;
    max-width: 420px;
    animation: slideUp 0.6s ease;
}

@keyframes slideUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Calculator Styles */
.calculator {
    background: var(--light-bg);
    border-radius: var(--radius);
    padding: 28px;
    box-shadow: var(--shadow-lg);
    transition: var(--transition);
}

.dark-mode .calculator {
    background: var(--dark-secondary-bg);
}

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

.display-section {
    margin-bottom: 28px;
    text-align: right;
    background: linear-gradient(135deg, var(--light-secondary-bg), var(--light-tertiary-bg));
    padding: 24px;
    border-radius: 18px;
    position: relative;
    transition: var(--transition);
    border: 1px solid rgba(255, 255, 255, 0.5);
}

.dark-mode .display-section {
    background: linear-gradient(135deg, var(--dark-tertiary-bg), #3C3C3E);
    border-color: rgba(255, 255, 255, 0.1);
}

.timer-icon {
    font-size: 14px;
    margin-bottom: 8px;
    opacity: 0.6;
    transition: var(--transition);
}

.previous-operand {
    font-size: 16px;
    min-height: 22px;
    opacity: 0.7;
    margin-bottom: 8px;
    font-weight: 500;
    color: var(--light-text-secondary);
    transition: var(--transition);
}

.dark-mode .previous-operand {
    color: var(--dark-text-secondary);
}

.current-display {
    font-size: 52px;
    font-weight: 700;
    word-wrap: break-word;
    word-break: break-all;
    min-height: 65px;
    display: flex;
    align-items: flex-end;
    justify-content: flex-end;
    letter-spacing: -1px;
    transition: var(--transition);
}

.buttons-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 14px;
}

.btn {
    padding: 20px;
    font-size: 18px;
    font-weight: 600;
    border: none;
    border-radius: 14px;
    cursor: pointer;
    transition: var(--transition);
    box-shadow: var(--shadow-sm);
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}

.light-calc .btn,
.calculator .btn {
    background: var(--button-light);
    color: var(--light-text);
}

.dark-mode .calculator .btn {
    background: var(--dark-tertiary-bg);
    color: var(--dark-text);
}

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

.btn:active {
    transform: scale(0.95);
}

.btn.number {
    font-weight: 500;
}

.btn.operation,
.btn.equals {
    background: linear-gradient(135deg, var(--primary-orange), var(--secondary-orange)) !important;
    color: white;
    font-weight: 700;
    box-shadow: 0 4px 16px rgba(255, 149, 0, 0.3);
}

.btn.operation:hover,
.btn.equals:hover {
    box-shadow: 0 8px 24px rgba(255, 149, 0, 0.5);
}

.btn.operator {
    font-size: 16px;
    opacity: 0.9;
}

.zero {
    grid-column: span 2;
}

/* Download Button */
.download-btn {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 64px;
    height: 64px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-orange), var(--secondary-orange));
    border: none;
    color: white;
    font-size: 28px;
    cursor: pointer;
    box-shadow: 0 8px 24px rgba(255, 149, 0, 0.4);
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 999;
}

.download-btn:hover {
    transform: scale(1.1);
    box-shadow: 0 12px 32px rgba(255, 149, 0, 0.6);
}

.download-btn:active {
    transform: scale(0.95);
}

/* History Modal */
.history-modal {
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%) scale(0.9);
    background: var(--light-bg);
    border-radius: var(--radius);
    width: 90%;
    max-width: 500px;
    max-height: 70vh;
    z-index: 2000;
    box-shadow: var(--shadow-lg);
    display: flex;
    flex-direction: column;
    opacity: 0;
    pointer-events: none;
    transition: var(--transition);
}

.dark-mode .history-modal {
    background: var(--dark-secondary-bg);
}

.history-modal.open {
    opacity: 1;
    pointer-events: all;
    transform: translate(-50%, -50%) scale(1);
}

.history-modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 24px;
    border-bottom: 1px solid var(--light-tertiary-bg);
}

.dark-mode .history-modal-header {
    border-bottom-color: var(--dark-tertiary-bg);
}

.history-modal-header h2 {
    font-size: 24px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-orange), var(--secondary-orange));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.close-history {
    background: none;
    border: none;
    font-size: 24px;
    cursor: pointer;
    color: var(--light-text-secondary);
    transition: var(--transition);
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 8px;
}

.dark-mode .close-history {
    color: var(--dark-text-secondary);
}

.close-history:hover {
    background: var(--light-secondary-bg);
    transform: scale(1.1);
}

.dark-mode .close-history:hover {
    background: var(--dark-tertiary-bg);
}

.history-modal-body {
    flex: 1;
    overflow-y: auto;
    padding: 20px;
}

.history-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.history-item {
    padding: 16px;
    background: var(--light-secondary-bg);
    border-radius: var(--radius-sm);
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
    transition: var(--transition);
    border: 1px solid transparent;
}

.dark-mode .history-item {
    background: var(--dark-tertiary-bg);
}

.history-item:hover {
    background: linear-gradient(135deg, var(--light-secondary-bg), var(--light-tertiary-bg));
    transform: translateX(6px);
    border-color: var(--primary-orange);
}

.dark-mode .history-item:hover {
    background: linear-gradient(135deg, var(--dark-tertiary-bg), #3C3C3E);
}

.history-item-left {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.history-calculation {
    font-size: 14px;
    color: var(--light-text-secondary);
    font-weight: 500;
}

.dark-mode .history-calculation {
    color: var(--dark-text-secondary);
}

.history-time {
    font-size: 12px;
    color: var(--light-text-secondary);
    opacity: 0.6;
}

.dark-mode .history-time {
    color: var(--dark-text-secondary);
}

.history-result {
    font-size: 18px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-orange), var(--secondary-orange));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.empty-history {
    text-align: center;
    color: var(--light-text-secondary);
    padding: 60px 20px;
    font-size: 16px;
}

.dark-mode .empty-history {
    color: var(--dark-text-secondary);
}

.history-modal-footer {
    padding: 20px;
    border-top: 1px solid var(--light-tertiary-bg);
}

.dark-mode .history-modal-footer {
    border-top-color: var(--dark-tertiary-bg);
}

.clear-history-btn {
    width: 100%;
    padding: 14px;
    background: linear-gradient(135deg, var(--primary-orange), var(--secondary-orange));
    color: white;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 16px;
    font-weight: 600;
    transition: var(--transition);
    box-shadow: var(--shadow-sm);
}

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

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

/* History Backdrop */
.history-backdrop {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0);
    z-index: 1500;
    opacity: 0;
    pointer-events: none;
    transition: var(--transition);
}

.history-backdrop.open {
    background: rgba(0, 0, 0, 0.5);
    opacity: 1;
    pointer-events: all;
}

/* Scrollbar Styling */
.history-modal-body::-webkit-scrollbar {
    width: 8px;
}

.history-modal-body::-webkit-scrollbar-track {
    background: transparent;
}

.history-modal-body::-webkit-scrollbar-thumb {
    background: var(--primary-orange);
    border-radius: 4px;
}

.history-modal-body::-webkit-scrollbar-thumb:hover {
    background: var(--secondary-orange);
}

/* Responsive Design */
@media (max-width: 768px) {
    .main-container {
        padding: 24px 16px;
    }

    .calculator {
        padding: 20px;
    }

    .current-display {
        font-size: 40px;
    }

    .btn {
        padding: 16px;
        font-size: 16px;
    }

    .buttons-grid {
        gap: 12px;
    }

    .download-btn {
        bottom: 20px;
        right: 20px;
        width: 56px;
        height: 56px;
        font-size: 24px;
    }

    .header-content {
        padding: 0 16px;
    }

    .history-modal {
        width: 95%;
        max-height: 80vh;
    }
}

@media (max-width: 480px) {
    .logo {
        font-size: 22px;
    }

    .header-controls {
        gap: 12px;
    }

    .history-btn .label {
        display: none;
    }

    .history-btn {
        padding: 8px 12px;
        width: 40px;
        height: 40px;
        justify-content: center;
    }

    .main-container {
        padding: 16px 12px;
    }

    .calculator {
        padding: 16px;
    }

    .display-section {
        padding: 16px;
        margin-bottom: 16px;
    }

    .current-display {
        font-size: 32px;
        min-height: 45px;
    }

    .previous-operand {
        font-size: 14px;
    }

    .btn {
        padding: 14px;
        font-size: 14px;
    }

    .buttons-grid {
        gap: 10px;
    }

    .theme-selector {
        gap: 6px;
        padding: 4px;
    }

    .theme-btn {
        width: 32px;
        height: 32px;
        font-size: 16px;
    }

    .download-btn {
        bottom: 16px;
        right: 16px;
        width: 48px;
        height: 48px;
        font-size: 20px;
    }

    .history-modal-header h2 {
        font-size: 20px;
    }

    .history-modal-header {
        padding: 16px;
    }

    .close-history {
        width: 32px;
        height: 32px;
        font-size: 20px;
    }
}

/* Animation Enhancements */
@keyframes fadeInScale {
    from {
        opacity: 0;
        transform: scale(0.95);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

.history-item {
    animation: fadeInScale 0.3s ease;
}