/* Base Styles & Color System */
:root {
    /* Color System */
    --color-bg-primary: #000000;
    --color-bg-card: #1A1A1A;
    --color-bg-card-hover: #212121;
    --color-text-primary: rgba(255, 255, 255, 0.95);
    --color-text-secondary: rgba(255, 255, 255, 0.75);
    --color-text-tertiary: rgba(255, 255, 255, 0.5);
    --color-emphasis: #FF9500;
    --color-emphasis-secondary: rgba(255, 149, 0, 0.75);
    --color-emphasis-light: rgba(255, 149, 0, 0.5);
    --color-emphasis-interactive: rgba(255, 149, 0, 0.85);
    --color-positive: #4CAF50;
    --color-negative: #FF3B30;
    --color-neutral: #8E8E93;
    
    /* Spacing System */
    --spacing-xs: 8px;
    --spacing-sm: 16px;
    --spacing-md: 24px;
    --spacing-lg: 32px;
    
    /* Border Radius */
    --radius-sm: 8px;
    --radius-md: 16px;
    
    /* Transitions */
    --transition-standard: 200ms cubic-bezier(0.16, 1, 0.3, 1);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background-color: var(--color-bg-primary);
    color: var(--color-text-primary);
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    font-feature-settings: "tnum";
    letter-spacing: -0.01em;
    padding: var(--spacing-md);
}

/* Typography */
h1 {
    font-size: clamp(2.5rem, 5vw, 3.5rem);
    font-weight: 700;
    margin-bottom: var(--spacing-md);
    color: var(--color-emphasis);
    text-align: center;
    line-height: 1.2;
}

h2 {
    font-size: clamp(1.5rem, 3vw, 2rem);
    font-weight: 600;
    margin: var(--spacing-md) 0 var(--spacing-sm);
    color: var(--color-text-primary);
}

h3 {
    font-size: clamp(1.1rem, 2vw, 1.3rem);
    font-weight: 600;
    margin: var(--spacing-sm) 0 var(--spacing-xs);
    color: var(--color-text-primary);
    line-height: 1.4;
}

p {
    margin-bottom: var(--spacing-sm);
    color: var(--color-text-secondary);
}

/* Layout */
.container {
    max-width: 1200px;
    margin: 0 auto;
}

header {
    margin-bottom: var(--spacing-lg);
    padding: var(--spacing-md) 0;
}

main {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-md);
}

@media (min-width: 768px) {
    main {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 1024px) {
    main {
        grid-template-columns: repeat(4, 1fr);
    }
}

/* Card System */
.card {
    background: linear-gradient(175deg, var(--color-bg-card), var(--color-bg-card-hover));
    border-radius: var(--radius-md);
    padding: clamp(var(--spacing-md), 4vw, var(--spacing-lg));
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
    position: relative;
    overflow: hidden;
    transition: var(--transition-standard);
}

.card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 1px;
    background: rgba(255, 255, 255, 0.07);
}

.card::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noiseFilter)'/%3E%3C/svg%3E");
    opacity: 0.03;
    pointer-events: none;
}

.card:hover {
    transform: scale(1.02);
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.4);
    background-color: var(--color-bg-card-hover);
}

.card:active {
    transform: translateY(1px) scale(1.01);
    filter: brightness(0.95);
}

/* Converter Card */
.converter-card {
    grid-column: 1 / -1;
}

.converter-container {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-md);
}

@media (min-width: 768px) {
    .converter-container {
        grid-template-columns: repeat(2, 1fr);
    }
}

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

.input-group label {
    font-size: 1rem;
    color: var(--color-text-secondary);
}

.input-wrapper {
    position: relative;
    display: flex;
    align-items: center;
    height: 80px;
}

input {
    width: 100%;
    height: 80px;
    padding: var(--spacing-sm);
    padding-right: 90px;
    font-size: clamp(1.5rem, 4vw, 2.5rem);
    background-color: rgba(255, 255, 255, 0.05);
    border: 1px solid rgba(255, 255, 255, 0.1);
    border-radius: var(--radius-sm);
    color: var(--color-text-primary);
    font-weight: 700;
    font-feature-settings: "tnum";
    transition: var(--transition-standard);
    appearance: none;
    -webkit-appearance: none;
    -moz-appearance: textfield;
}

input::-webkit-inner-spin-button, 
input::-webkit-outer-spin-button { 
    -webkit-appearance: none;
    margin: 0;
}

input:focus {
    outline: none;
    border-color: var(--color-emphasis);
    box-shadow: 0 0 0 2px rgba(255, 149, 0, 0.25);
}

input:hover {
    border-color: rgba(255, 255, 255, 0.1);
}

.unit {
    position: absolute;
    right: var(--spacing-sm);
    top: 50%;
    transform: translateY(-50%);
    color: var(--color-emphasis);
    font-weight: 600;
    font-size: 1.2rem;
    pointer-events: none;
}

/* Keywords Card */
.keywords-card {
    grid-column: 1 / -1;
}

.keywords-list {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--spacing-sm);
    list-style: none;
}

@media (min-width: 768px) {
    .keywords-list {
        grid-template-columns: repeat(3, 1fr);
    }
}

@media (min-width: 1024px) {
    .keywords-list {
        grid-template-columns: repeat(5, 1fr);
    }
}

.keywords-list li {
    margin-bottom: var(--spacing-xs);
}

.keywords-list a {
    display: block;
    color: var(--color-text-secondary);
    text-decoration: none;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    background-color: rgba(255, 255, 255, 0.05);
    border: 1px solid rgba(255, 255, 255, 0.1);
    transition: var(--transition-standard);
    font-size: 0.9rem;
}

.keywords-list a:hover {
    background-color: rgba(255, 149, 0, 0.15);
    border-color: var(--color-emphasis-light);
    color: var(--color-emphasis);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(255, 149, 0, 0.15);
}

.keywords-list a:active {
    transform: translateY(0);
}

/* Information Cards */
.info-card {
    display: flex;
    flex-direction: column;
    font-size: 0.95rem;
    height: 100%;
}

.info-card h2 {
    color: var(--color-emphasis);
    margin-bottom: var(--spacing-sm);
    font-size: clamp(1.2rem, 2vw, 1.5rem);
}

.info-card h3 {
    font-size: clamp(1.1rem, 2vw, 1.3rem);
    font-weight: 600;
    margin: var(--spacing-sm) 0 var(--spacing-xs);
    color: var(--color-text-primary);
    line-height: 1.4;
}

/* FAQ 项目中的 H3 特殊样式(为后续FAQ准备) */
.faq-item h3 {
    color: var(--color-emphasis-secondary);
    margin-bottom: var(--spacing-xs);
}

.info-card p {
    font-size: 0.9rem;
    line-height: 1.4;
}

/* Responsive adjustments for info cards */
@media (max-width: 1023px) {
    .info-card {
        grid-column: span 2;
    }
}

@media (max-width: 767px) {
    .info-card {
        grid-column: 1 / -1;
    }
}

/* Formula Display */
.formula {
    display: inline-block;
    background-color: rgba(255, 255, 255, 0.05);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    margin: var(--spacing-xs) 0;
    font-family: monospace;
    color: var(--color-emphasis-secondary);
}

/* Table Styles */
.conversion-table {
    width: 100%;
    border-collapse: collapse;
    margin: var(--spacing-sm) 0;
    font-size: 0.85rem;
}

.conversion-table th,
.conversion-table td {
    padding: var(--spacing-xs) var(--spacing-sm);
    text-align: left;
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.conversion-table th {
    color: var(--color-emphasis-light);
    font-weight: 600;
}

/* Footer */
footer {
    margin-top: var(--spacing-lg);
    padding: var(--spacing-md) 0;
    text-align: center;
    color: var(--color-text-tertiary);
    font-size: 0.9rem;
}

/* Animations */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(15px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.card {
    animation: fadeInUp 300ms cubic-bezier(0.2, 0.8, 0.2, 1) forwards;
    animation-delay: calc(var(--animation-order) * 30ms);
}

.converter-card {
    --animation-order: 1;
}

.keywords-card {
    --animation-order: 2;
}

.info-card:nth-of-type(1) {
    --animation-order: 3;
}

.info-card:nth-of-type(2) {
    --animation-order: 4;
}

.info-card:nth-of-type(3) {
    --animation-order: 5;
}

.info-card:nth-of-type(4) {
    --animation-order: 6;
}

/* Breadcrumb Navigation */
.breadcrumb {
    padding: var(--spacing-xs) 0 var(--spacing-sm);
    font-size: 0.9rem;
}

.breadcrumb ol {
    list-style: none;
    display: flex;
    gap: var(--spacing-xs);
    align-items: center;
}

.breadcrumb li:not(:last-child)::after {
    content: '›';
    margin-left: var(--spacing-xs);
    color: var(--color-text-tertiary);
}

.breadcrumb a {
    color: var(--color-emphasis);
    text-decoration: none;
    transition: var(--transition-standard);
}

.breadcrumb a:hover {
    text-decoration: underline;
    color: var(--color-emphasis-interactive);
}

.breadcrumb li[aria-current="page"] {
    color: var(--color-text-secondary);
}

/* FAQ Styles */
.faq-item {
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-sm);
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.faq-item:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}

.faq-item h3 {
    color: var(--color-emphasis-secondary);
    margin-bottom: var(--spacing-xs);
}

.faq-item p {
    margin-bottom: var(--spacing-xs);
}

/* Accessibility: Skip Navigation Link */
.skip-link {
    position: absolute;
    top: -40px;
    left: 0;
    background: var(--color-emphasis);
    color: #000000;
    padding: 8px 16px;
    text-decoration: none;
    font-weight: 600;
    z-index: 1000;
    border-radius: 0 0 4px 0;
}

.skip-link:focus {
    top: 0;
}

/* Accessibility: Visually Hidden (screen reader only) */
.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;
}