/* ===================================
   CSS Variables & Reset
   =================================== */
:root {
    /* Light Mode Colors */
    --primary-color: #6366f1;
    --primary-hover: #4f46e5;
    --secondary-color: #8b5cf6;
    --accent-color: #ec4899;
    
    --bg-gradient-1: #667eea;
    --bg-gradient-2: #764ba2;
    --bg-gradient-3: #f093fb;
    
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --text-light: #9ca3af;
    
    --card-bg: rgba(255, 255, 255, 0.85);
    --card-border: rgba(255, 255, 255, 0.3);
    --input-bg: rgba(255, 255, 255, 0.6);
    --input-border: rgba(209, 213, 219, 0.5);
    --input-focus: rgba(99, 102, 241, 0.3);
    
    --success-color: #10b981;
    --error-color: #ef4444;
    
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    
    --border-radius: 16px;
    --border-radius-sm: 8px;
    --border-radius-lg: 24px;
    
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-fast: all 0.15s ease;
}

/* Dark Mode Colors */
body.dark-mode {
    --bg-gradient-1: #1e1b4b;
    --bg-gradient-2: #312e81;
    --bg-gradient-3: #4c1d95;
    
    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --text-light: #9ca3af;
    
    --card-bg: rgba(31, 41, 55, 0.85);
    --card-border: rgba(75, 85, 99, 0.3);
    --input-bg: rgba(55, 65, 81, 0.6);
    --input-border: rgba(75, 85, 99, 0.5);
    --input-focus: rgba(99, 102, 241, 0.4);
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
    transition: var(--transition);
    min-height: 100vh;
}

/* ===================================
   Background Gradient
   =================================== */
.background-gradient {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: -1;
    background: linear-gradient(135deg, 
        var(--bg-gradient-1) 0%, 
        var(--bg-gradient-2) 50%, 
        var(--bg-gradient-3) 100%);
    animation: gradientShift 15s ease infinite;
}

@keyframes gradientShift {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.9; }
}

/* ===================================
   Container & Layout
   =================================== */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem 1rem;
    position: relative;
    z-index: 1;
}

/* ===================================
   Hero Section
   =================================== */
.hero {
    text-align: center;
    margin-bottom: 3rem;
    animation: fadeInDown 0.6s ease;
}

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

.hero-title {
    font-size: clamp(2.5rem, 5vw, 3.5rem);
    font-weight: 700;
    color: white;
    margin-bottom: 0.5rem;
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
    letter-spacing: -0.02em;
}

.hero-subtitle {
    font-size: clamp(1rem, 2vw, 1.25rem);
    color: rgba(255, 255, 255, 0.9);
    font-weight: 400;
    max-width: 600px;
    margin: 0 auto;
    text-shadow: 0 1px 5px rgba(0, 0, 0, 0.15);
}

/* ===================================
   Calculator Card - Glassmorphism
   =================================== */
.calculator-card {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-radius: var(--border-radius-lg);
    border: 1px solid var(--card-border);
    box-shadow: var(--shadow-xl), 
                0 0 0 1px rgba(255, 255, 255, 0.1) inset;
    padding: 2.5rem;
    max-width: 600px;
    margin: 0 auto 4rem;
    position: relative;
    animation: fadeInUp 0.7s ease;
}

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

/* ===================================
   Mode Toggle
   =================================== */
.mode-toggle {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.75rem;
    margin-bottom: 2rem;
    padding: 0.5rem;
    background: var(--input-bg);
    border-radius: var(--border-radius);
    backdrop-filter: blur(10px);
}

.mode-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 0.875rem 1rem;
    border: none;
    border-radius: var(--border-radius-sm);
    background: transparent;
    color: var(--text-secondary);
    font-size: 0.95rem;
    font-weight: 500;
    font-family: inherit;
    cursor: pointer;
    transition: var(--transition);
    position: relative;
}

.mode-btn:hover {
    background: rgba(255, 255, 255, 0.1);
    color: var(--text-primary);
}

.mode-btn.active {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    box-shadow: var(--shadow-md);
}

.mode-icon {
    width: 18px;
    height: 18px;
}

/* ===================================
   Form Elements
   =================================== */
.calculator-form {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.form-label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-primary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

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

.currency-symbol {
    position: absolute;
    left: 1rem;
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-secondary);
    pointer-events: none;
    z-index: 1;
}

.form-input {
    width: 100%;
    padding: 1rem 1rem 1rem 2.5rem;
    border: 2px solid var(--input-border);
    border-radius: var(--border-radius);
    background: var(--input-bg);
    backdrop-filter: blur(10px);
    font-size: 1.125rem;
    font-weight: 500;
    font-family: inherit;
    color: var(--text-primary);
    transition: var(--transition);
    outline: none;
}

.form-input::placeholder {
    color: var(--text-light);
}

.form-input:focus {
    border-color: var(--primary-color);
    background: rgba(255, 255, 255, 0.8);
    box-shadow: 0 0 0 4px var(--input-focus);
    transform: translateY(-1px);
}

body.dark-mode .form-input:focus {
    background: rgba(55, 65, 81, 0.8);
}

/* ===================================
   VAT Rate Selection
   =================================== */
.vat-rate-container {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.preset-rates {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 0.5rem;
}

.rate-btn {
    padding: 0.75rem;
    border: 2px solid var(--input-border);
    border-radius: var(--border-radius-sm);
    background: var(--input-bg);
    backdrop-filter: blur(10px);
    font-size: 0.95rem;
    font-weight: 600;
    font-family: inherit;
    color: var(--text-secondary);
    cursor: pointer;
    transition: var(--transition);
}

.rate-btn:hover {
    border-color: var(--primary-color);
    color: var(--text-primary);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.rate-btn.active {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border-color: transparent;
    color: white;
    box-shadow: var(--shadow-md);
}

.custom-rate {
    position: relative;
}

.custom-rate-input {
    padding-right: 2.5rem !important;
    padding-left: 1rem !important;
}

.percent-symbol {
    position: absolute;
    right: 1rem;
    top: 50%;
    transform: translateY(-50%);
    font-weight: 600;
    color: var(--text-secondary);
    pointer-events: none;
}

/* ===================================
   Results Display
   =================================== */
.results {
    background: var(--input-bg);
    backdrop-filter: blur(10px);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
    border: 1px solid var(--input-border);
}

.result-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.75rem 0;
    border-bottom: 1px solid var(--input-border);
    transition: var(--transition);
}

.result-item:last-child {
    border-bottom: none;
}

.result-item.highlight {
    padding: 1rem;
    background: linear-gradient(135deg, 
        rgba(99, 102, 241, 0.1), 
        rgba(139, 92, 246, 0.1));
    border-radius: var(--border-radius-sm);
    border-bottom: none;
    margin: 0.25rem 0;
}

.result-item.total {
    padding-top: 1rem;
    margin-top: 0.5rem;
}

.result-label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.03em;
}

.result-value {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
    font-variant-numeric: tabular-nums;
}

.result-item.total .result-value {
    font-size: 1.5rem;
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* ===================================
   Action Buttons
   =================================== */
.action-buttons {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.75rem;
    margin-top: 0.5rem;
}

.btn {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 1rem 1.5rem;
    border: none;
    border-radius: var(--border-radius);
    font-size: 0.95rem;
    font-weight: 600;
    font-family: inherit;
    cursor: pointer;
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.3);
    transform: translate(-50%, -50%);
    transition: width 0.6s, height 0.6s;
}

.btn:active::before {
    width: 300px;
    height: 300px;
}

.btn-icon {
    width: 18px;
    height: 18px;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    box-shadow: var(--shadow-md);
}

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

.btn-secondary {
    background: var(--input-bg);
    backdrop-filter: blur(10px);
    color: var(--text-primary);
    border: 2px solid var(--input-border);
}

.btn-secondary:hover {
    border-color: var(--primary-color);
    background: rgba(255, 255, 255, 0.5);
    transform: translateY(-2px);
}

/* Copy Button Success State */
.btn-primary.copied {
    background: linear-gradient(135deg, var(--success-color), #059669);
}

/* ===================================
   Dark Mode Toggle
   =================================== */
.dark-mode-toggle {
    position: absolute;
    top: 1.5rem;
    right: 1.5rem;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    border: 2px solid var(--input-border);
    background: var(--input-bg);
    backdrop-filter: blur(10px);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
    z-index: 10;
}

.dark-mode-toggle:hover {
    transform: scale(1.1) rotate(10deg);
    border-color: var(--primary-color);
    box-shadow: var(--shadow-md);
}

.dark-mode-toggle svg {
    width: 20px;
    height: 20px;
    position: absolute;
    transition: var(--transition);
}

.sun-icon {
    opacity: 1;
    transform: rotate(0deg);
}

.moon-icon {
    opacity: 0;
    transform: rotate(180deg);
}

body.dark-mode .sun-icon {
    opacity: 0;
    transform: rotate(180deg);
}

body.dark-mode .moon-icon {
    opacity: 1;
    transform: rotate(0deg);
}

/* ===================================
   How to Use Section
   =================================== */
.how-to-use {
    max-width: 900px;
    margin: 0 auto 4rem;
    animation: fadeInUp 0.8s ease 0.2s both;
}

.section-title {
    text-align: center;
    font-size: 2rem;
    font-weight: 700;
    color: white;
    margin-bottom: 2.5rem;
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
}

.steps {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
}

.step {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius);
    border: 1px solid var(--card-border);
    padding: 1.5rem;
    transition: var(--transition);
}

.step:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-xl);
}

.step-number {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 1.125rem;
    margin-bottom: 1rem;
    box-shadow: var(--shadow-md);
}

.step-content h3 {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
}

.step-content p {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

/* ===================================
   Footer
   =================================== */
.footer {
    text-align: center;
    padding: 2rem 0;
    color: rgba(255, 255, 255, 0.8);
    font-size: 0.875rem;
}

/* ===================================
   Responsive Design
   =================================== */
@media (max-width: 768px) {
    .container {
        padding: 1.5rem 1rem;
    }
    
    .calculator-card {
        padding: 1.5rem;
        margin-bottom: 3rem;
    }
    
    .action-buttons {
        grid-template-columns: 1fr;
    }
    
    .preset-rates {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .steps {
        grid-template-columns: 1fr;
    }
    
    .dark-mode-toggle {
        top: 1rem;
        right: 1rem;
        width: 40px;
        height: 40px;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 2rem;
    }
    
    .mode-toggle {
        gap: 0.5rem;
        padding: 0.375rem;
    }
    
    .mode-btn {
        padding: 0.75rem 0.5rem;
        font-size: 0.875rem;
    }
    
    .mode-icon {
        width: 16px;
        height: 16px;
    }
}

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

/* Focus visible for keyboard navigation */
.btn:focus-visible,
.mode-btn:focus-visible,
.rate-btn:focus-visible,
.dark-mode-toggle:focus-visible {
    outline: 3px solid var(--primary-color);
    outline-offset: 2px;
}

/* High contrast mode support */
@media (prefers-contrast: high) {
    .calculator-card {
        border: 2px solid var(--text-primary);
    }
    
    .form-input {
        border-width: 2px;
    }
}

/* ===================================
   Content Sections Styling
   =================================== */
.content-section {
    max-width: 900px;
    margin: 0 auto 4rem;
    animation: fadeInUp 0.8s ease 0.3s both;
}

.content-card {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius);
    border: 1px solid var(--card-border);
    padding: 2rem;
    color: var(--text-primary);
    line-height: 1.8;
}

.content-card p {
    margin-bottom: 1.25rem;
    color: var(--text-primary);
}

.content-card strong {
    color: var(--text-primary);
    font-weight: 600;
}

.vat-rates-list {
    list-style: none;
    padding: 0;
    margin: 1.5rem 0;
}

.vat-rates-list li {
    padding: 1rem;
    margin-bottom: 0.75rem;
    background: var(--input-bg);
    border-radius: var(--border-radius-sm);
    border-left: 4px solid var(--primary-color);
    transition: var(--transition);
}

.vat-rates-list li:hover {
    transform: translateX(5px);
    border-left-color: var(--secondary-color);
}

.examples-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
}

.example-card {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius);
    border: 1px solid var(--card-border);
    padding: 1.75rem;
    transition: var(--transition);
}

.example-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-xl);
    border-color: var(--primary-color);
}

.example-card h3 {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 1rem;
    padding-bottom: 0.75rem;
    border-bottom: 2px solid var(--input-border);
}

.example-card p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-bottom: 0.75rem;
    line-height: 1.6;
}

.example-card ul {
    list-style: none;
    padding: 0;
    margin: 0.75rem 0 0 0;
}

.example-card ul li {
    padding: 0.5rem 0;
    color: var(--text-primary);
    font-family: 'Courier New', monospace;
    font-size: 0.9rem;
}

.faq-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
}

.faq-item {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius);
    border: 1px solid var(--card-border);
    padding: 1.75rem;
    transition: var(--transition);
}

.faq-item:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-lg);
    border-color: var(--primary-color);
}

.faq-item h3 {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.75rem;
    display: flex;
    align-items: flex-start;
}

.faq-item h3::before {
    content: "Q";
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    font-size: 0.75rem;
    font-weight: 700;
    margin-right: 0.75rem;
    flex-shrink: 0;
}

.faq-item p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.7;
}

.modes-comparison {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.mode-card {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius);
    border: 1px solid var(--card-border);
    padding: 2rem;
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.mode-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
}

.mode-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-xl);
}

.mode-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 1rem;
}

.mode-card p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-bottom: 1rem;
}

.mode-card ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.mode-card ul li {
    padding: 0.625rem 0 0.625rem 1.75rem;
    color: var(--text-primary);
    font-size: 0.95rem;
    position: relative;
    line-height: 1.6;
}

.mode-card ul li::before {
    content: "✓";
    position: absolute;
    left: 0;
    color: var(--success-color);
    font-weight: 700;
    font-size: 1.1rem;
}

.footer-note {
    font-size: 0.8rem;
    color: rgba(255, 255, 255, 0.6);
    font-style: italic;
}

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

@media (max-width: 768px) {
    .examples-grid,
    .faq-grid,
    .modes-comparison {
        grid-template-columns: 1fr;
    }
    
    .content-card,
    .example-card,
    .faq-item,
    .mode-card {
        padding: 1.5rem;
    }
    
    .content-section {
        margin-bottom: 3rem;
    }
}

@media (max-width: 480px) {
    .vat-rates-list li {
        padding: 0.75rem;
        font-size: 0.9rem;
    }
}