/* ===================================
   CSS Variables & Reset
   =================================== */
:root {
    /* Brand Colors */
    --primary: #ff914d;
    --primary-dark: #ff711a;
    --primary-light: #fff6ed;
    --success: #12b981;
    --error: #ef4444;
    --text-primary: #1f2937;
    --text-secondary: #343a40;
    --text-muted: #6b7280;

    /* Neutral Colors */
    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-tertiary: #f3f4f6;
    --border-color: #e5e7eb;
    --border-color-hover: #d1d5db;

    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);

    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-base: 250ms ease-in-out;
    --transition-slow: 350ms ease-in-out;

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;

    /* Typography */
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 2rem;

    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-full: 9999px;
}

/* Reset & Base Styles */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: var(--text-primary);
    background: linear-gradient(135deg, var(--primary-light) 0%, #ffffff 50%, var(--bg-secondary) 100%);
    background-attachment: fixed;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* ===================================
   Layout & Container
   =================================== */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* ===================================
   Header
   =================================== */
.header {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: white;
    padding: var(--spacing-2xl) var(--spacing-md);
    text-align: center;
    box-shadow: var(--shadow-md);
    margin-bottom: var(--spacing-2xl);
}

.logo {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    font-size: var(--font-size-3xl);
    font-weight: 700;
    margin-bottom: var(--spacing-sm);
}

.logo-icon {
    font-size: 2.5rem;
    animation: rotate 3s linear infinite;
}

@keyframes rotate {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}

.subtitle {
    font-size: var(--font-size-lg);
    opacity: 0.95;
    font-weight: 400;
}

/* ===================================
   Main Content
   =================================== */
.main-content {
    padding-bottom: var(--spacing-2xl);
}

/* ===================================
   Category Navigation
   =================================== */
.category-nav {
    margin-bottom: var(--spacing-2xl);
}

.category-tabs {
    display: flex;
    gap: var(--spacing-sm);
    flex-wrap: wrap;
    justify-content: center;
    background: var(--bg-primary);
    padding: var(--spacing-md);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-lg);
}

.category-tab {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-md) var(--spacing-lg);
    border: 2px solid transparent;
    background: var(--bg-secondary);
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-base);
    font-size: var(--font-size-sm);
    font-weight: 500;
    color: var(--text-secondary);
    min-width: 90px;
}

.category-tab:hover {
    background: var(--primary-light);
    border-color: var(--primary);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.category-tab.active {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: white;
    border-color: var(--primary-dark);
    box-shadow: var(--shadow-md);
}

.category-tab:focus-visible {
    outline: 2px solid var(--primary);
    outline-offset: 2px;
}

.tab-icon {
    font-size: var(--font-size-2xl);
    transition: transform var(--transition-base);
}

.category-tab:hover .tab-icon {
    transform: scale(1.1);
}

.tab-label {
    font-weight: 600;
    white-space: nowrap;
}

/* ===================================
   Conversion Panel
   =================================== */
.conversion-panel {
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-2xl);
    box-shadow: var(--shadow-xl);
    margin-bottom: var(--spacing-2xl);
    animation: fadeInUp 0.5s ease-out;
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.conversion-group {
    margin-bottom: var(--spacing-xl);
}

.conversion-label {
    display: block;
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
}

.conversion-input-group {
    display: grid;
    grid-template-columns: 1fr auto 48px;
    gap: var(--spacing-md);
    align-items: stretch;
}

.conversion-input {
    padding: var(--spacing-lg);
    font-size: var(--font-size-xl);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    background: var(--bg-primary);
    color: var(--text-primary);
    transition: all var(--transition-base);
    font-family: var(--font-family);
    font-weight: 500;
}

.conversion-input:hover {
    border-color: var(--border-color-hover);
}

.conversion-input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(255, 145, 77, 0.1);
}

.conversion-input[readonly] {
    background: var(--bg-secondary);
    cursor: default;
}

/* Chrome, Safari, Edge, Opera - Remove spinner */
.conversion-input::-webkit-outer-spin-button,
.conversion-input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

/* Firefox - Remove spinner */
.conversion-input[type=number] {
    -moz-appearance: textfield;
}

.conversion-select {
    padding: var(--spacing-lg);
    font-size: var(--font-size-base);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    background: var(--bg-primary);
    color: var(--text-primary);
    cursor: pointer;
    transition: all var(--transition-base);
    font-family: var(--font-family);
    font-weight: 500;
    min-width: 140px;
}

.conversion-select:hover {
    border-color: var(--border-color-hover);
}

.conversion-select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(255, 145, 77, 0.1);
}

.copy-btn {
    padding: var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    background: var(--bg-primary);
    color: var(--text-muted);
    cursor: pointer;
    transition: all var(--transition-base);
    display: flex;
    align-items: center;
    justify-content: center;
}

.copy-btn:hover {
    background: var(--primary);
    border-color: var(--primary);
    color: white;
    transform: scale(1.05);
}

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

.copy-btn:focus-visible {
    outline: 2px solid var(--primary);
    outline-offset: 2px;
}

/* ===================================
   Swap Button
   =================================== */
.swap-container {
    display: flex;
    justify-content: center;
    margin: var(--spacing-lg) 0;
}

.swap-btn {
    width: 56px;
    height: 56px;
    border-radius: var(--radius-full);
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: white;
    border: none;
    cursor: pointer;
    transition: all var(--transition-base);
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow-lg);
}

.swap-btn:hover {
    transform: rotate(180deg) scale(1.1);
    box-shadow: var(--shadow-xl);
}

.swap-btn:active {
    transform: rotate(180deg) scale(0.95);
}

.swap-btn:focus-visible {
    outline: 3px solid var(--primary);
    outline-offset: 3px;
}

/* ===================================
   Conversion Info
   =================================== */
.conversion-info {
    margin-top: var(--spacing-xl);
    padding: var(--spacing-lg);
    background: linear-gradient(135deg, var(--primary-light) 0%, rgba(255, 145, 77, 0.05) 100%);
    border-left: 4px solid var(--primary);
    border-radius: var(--radius-md);
    font-size: var(--font-size-sm);
    color: var(--text-secondary);
    line-height: 1.6;
}

.conversion-info.empty {
    display: none;
}

.conversion-formula {
    font-family: 'Courier New', monospace;
    background: rgba(255, 145, 77, 0.1);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-sm);
    display: inline-block;
    margin-top: var(--spacing-sm);
}

/* ===================================
   History Section
   =================================== */
.history-section {
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-2xl);
    box-shadow: var(--shadow-lg);
    margin-bottom: var(--spacing-2xl);
}

.history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
}

.history-title {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--text-primary);
}

.clear-history-btn {
    padding: var(--spacing-sm) var(--spacing-lg);
    background: var(--bg-secondary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-base);
}

.clear-history-btn:hover {
    background: var(--error);
    border-color: var(--error);
    color: white;
}

.clear-history-btn:focus-visible {
    outline: 2px solid var(--error);
    outline-offset: 2px;
}

.history-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.history-empty {
    text-align: center;
    padding: var(--spacing-2xl);
    color: var(--text-muted);
    font-size: var(--font-size-base);
}

.history-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-lg);
    background: var(--bg-secondary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    transition: all var(--transition-base);
    animation: slideIn 0.3s ease-out;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-20px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.history-item:hover {
    border-color: var(--primary);
    box-shadow: var(--shadow-md);
    transform: translateX(4px);
}

.history-content {
    flex: 1;
}

.history-conversion {
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
}

.history-category {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
}

.history-actions {
    display: flex;
    gap: var(--spacing-sm);
}

.history-use-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    background: var(--primary);
    border: none;
    border-radius: var(--radius-md);
    color: white;
    font-size: var(--font-size-sm);
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-base);
}

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

.history-delete-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    background: transparent;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-muted);
    cursor: pointer;
    transition: all var(--transition-base);
    display: flex;
    align-items: center;
    justify-content: center;
}

.history-delete-btn:hover {
    background: var(--error);
    border-color: var(--error);
    color: white;
}

/* ===================================
   Keyboard Shortcuts Info
   =================================== */
.shortcuts-info {
    text-align: center;
    margin-bottom: var(--spacing-xl);
}

.shortcuts-toggle {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-xl);
    background: var(--bg-primary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-full);
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-base);
    box-shadow: var(--shadow-sm);
}

.shortcuts-toggle:hover {
    background: var(--primary-light);
    border-color: var(--primary);
    color: var(--primary-dark);
    box-shadow: var(--shadow-md);
}

.shortcuts-toggle:focus-visible {
    outline: 2px solid var(--primary);
    outline-offset: 2px;
}

/* ===================================
   Modal
   =================================== */
.modal {
    position: fixed;
    inset: 0;
    z-index: 1000;
    display: none;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-md);
}

.modal.active {
    display: flex;
}

.modal-overlay {
    position: absolute;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
    animation: fadeIn 0.2s ease-out;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.modal-content {
    position: relative;
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-xl);
    max-width: 500px;
    width: 100%;
    max-height: 90vh;
    overflow: auto;
    animation: modalSlideIn 0.3s ease-out;
}

@keyframes modalSlideIn {
    from {
        opacity: 0;
        transform: translateY(-20px) scale(0.95);
    }
    to {
        opacity: 1;
        transform: translateY(0) scale(1);
    }
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-xl);
    border-bottom: 2px solid var(--border-color);
}

.modal-header h2 {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--text-primary);
}

.modal-close {
    width: 40px;
    height: 40px;
    border: none;
    background: transparent;
    color: var(--text-muted);
    cursor: pointer;
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
    display: flex;
    align-items: center;
    justify-content: center;
}

.modal-close:hover {
    background: var(--bg-secondary);
    color: var(--text-primary);
}

.modal-body {
    padding: var(--spacing-xl);
}

.shortcut-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.shortcut-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-md);
    background: var(--bg-secondary);
    border-radius: var(--radius-md);
}

.kbd {
    display: inline-block;
    padding: var(--spacing-xs) var(--spacing-sm);
    background: var(--bg-primary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: var(--font-size-sm);
    font-weight: 600;
    font-family: monospace;
    box-shadow: var(--shadow-sm);
}

/* ===================================
   Toast Notification
   =================================== */
.toast {
    position: fixed;
    bottom: var(--spacing-xl);
    left: 50%;
    transform: translateX(-50%) translateY(100px);
    background: var(--text-primary);
    color: white;
    padding: var(--spacing-lg) var(--spacing-xl);
    border-radius: var(--radius-full);
    box-shadow: var(--shadow-xl);
    font-size: var(--font-size-sm);
    font-weight: 600;
    z-index: 2000;
    opacity: 0;
    transition: all var(--transition-base);
    max-width: 90vw;
}

.toast.show {
    transform: translateX(-50%) translateY(0);
    opacity: 1;
}

.toast.success {
    background: var(--success);
}

.toast.error {
    background: var(--error);
}

/* ===================================
   Footer
   =================================== */
.footer {
    background: var(--bg-primary);
    padding: var(--spacing-xl);
    text-align: center;
    color: var(--text-muted);
    font-size: var(--font-size-sm);
    box-shadow: var(--shadow-md);
}

/* ===================================
   Responsive Design
   =================================== */
@media (max-width: 768px) {
    .header {
        padding: var(--spacing-xl) var(--spacing-md);
    }

    .logo {
        font-size: var(--font-size-2xl);
        flex-direction: column;
        gap: var(--spacing-sm);
    }

    .logo-icon {
        font-size: 2rem;
    }

    .subtitle {
        font-size: var(--font-size-base);
    }

    .category-tabs {
        gap: var(--spacing-xs);
        padding: var(--spacing-sm);
    }

    .category-tab {
        min-width: 70px;
        padding: var(--spacing-sm) var(--spacing-md);
    }

    .tab-icon {
        font-size: var(--font-size-xl);
    }

    .tab-label {
        font-size: var(--font-size-xs);
    }

    .conversion-panel {
        padding: var(--spacing-lg);
    }

    .conversion-input-group {
        grid-template-columns: 1fr;
        gap: var(--spacing-sm);
    }

    .conversion-input,
    .conversion-select {
        font-size: var(--font-size-base);
    }

    .conversion-select {
        min-width: 100%;
    }

    .history-section {
        padding: var(--spacing-lg);
    }

    .history-item {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-md);
    }

    .history-actions {
        width: 100%;
    }

    .history-use-btn,
    .history-delete-btn {
        flex: 1;
    }
}

@media (max-width: 480px) {
    .category-tabs {
        justify-content: flex-start;
        overflow-x: auto;
        flex-wrap: nowrap;
        padding-bottom: var(--spacing-md);
        -webkit-overflow-scrolling: touch;
    }

    .category-tab {
        flex-shrink: 0;
    }

    .conversion-label {
        font-size: var(--font-size-base);
    }

    .swap-btn {
        width: 48px;
        height: 48px;
    }
}

/* ===================================
   Accessibility
   =================================== */
.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
}

/* Focus styles for keyboard navigation */
*:focus-visible {
    outline: 2px solid var(--primary);
    outline-offset: 2px;
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }

    .logo-icon {
        animation: none;
    }
}

/* ===================================
   Print Styles
   =================================== */
@media print {
    .header,
    .category-nav,
    .swap-container,
    .history-section,
    .shortcuts-info,
    .footer,
    .copy-btn {
        display: none;
    }

    .conversion-panel {
        box-shadow: none;
        border: 2px solid var(--border-color);
    }
}