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

:root {
    /* Color Palette */
    --primary-color: #1A535C;
    --secondary-color: #4ECDC4;
    --background-color: #F7FFF7;
    --accent-color: #FF6B6B;
    --warning-color: #FFE66D;
    
    /* Light Theme Colors */
    --text-primary: #1A535C;
    --text-secondary: #2d6a75;
    --text-muted: #6b8a92;
    --border-color: #e0f2f1;
    --card-background: #ffffff;
    --input-background: #ffffff;
    --shadow-color: rgba(26, 83, 92, 0.1);
    
    /* Typography */
    --font-family: 'Segoe UI', Tahoma, Geneva, Verdana, 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;
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    /* Transitions */
    --transition-fast: 0.15s ease-in-out;
    --transition-normal: 0.3s ease-in-out;
    --transition-slow: 0.5s ease-in-out;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 var(--shadow-color);
    --shadow-md: 0 4px 6px -1px var(--shadow-color);
    --shadow-lg: 0 10px 15px -3px var(--shadow-color);
    --shadow-xl: 0 20px 25px -5px var(--shadow-color);
}

/* Dark Theme */
[data-theme="dark"] {
    --background-color: #0f2027;
    --text-primary: #F7FFF7;
    --text-secondary: #e0f2f1;
    --text-muted: #b0bec5;
    --border-color: #2d4a52;
    --card-background: #1a3a42;
    --input-background: #2d4a52;
    --shadow-color: rgba(0, 0, 0, 0.3);
}

/* Base HTML and Body */
html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--background-color);
    transition: background-color var(--transition-normal), color var(--transition-normal);
    min-height: 100vh;
    overflow-x: hidden;
}

/* App Container */
.app-container {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header Styles */
.header {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: var(--spacing-lg) 0;
    box-shadow: var(--shadow-md);
    position: relative;
    overflow: hidden;
}

.header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100"><circle cx="50" cy="50" r="2" fill="rgba(255,255,255,0.1)"/></svg>') repeat;
    opacity: 0.3;
}

.header__content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: relative;
    z-index: 1;
}

.header__title {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin: 0;
}

.header__icon {
    font-size: var(--font-size-3xl);
    animation: bounce 2s infinite;
}

@keyframes bounce {
    0%, 20%, 50%, 80%, 100% {
        transform: translateY(0);
    }
    40% {
        transform: translateY(-10px);
    }
    60% {
        transform: translateY(-5px);
    }
}

/* Theme Toggle */
.theme-toggle {
    background: rgba(255, 255, 255, 0.2);
    border: 2px solid rgba(255, 255, 255, 0.3);
    border-radius: 50%;
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--transition-normal);
    backdrop-filter: blur(10px);
}

.theme-toggle:hover {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1.1);
}

.theme-toggle__icon {
    font-size: var(--font-size-xl);
    transition: transform var(--transition-normal);
}

.theme-toggle:active .theme-toggle__icon {
    transform: rotate(180deg);
}

/* Main Content */
.main {
    flex: 1;
    padding: var(--spacing-2xl) 0;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* Calculator Sections */
.calculator-section {
    margin-bottom: var(--spacing-2xl);
}

/* Card Component */
.card {
    background: var(--card-background);
    border-radius: var(--radius-xl);
    padding: var(--spacing-2xl);
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border-color);
    transition: all var(--transition-normal);
    position: relative;
    overflow: hidden;
}

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

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

.card__title {
    font-size: var(--font-size-2xl);
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xl);
    text-align: center;
    position: relative;
}

.card__title::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 50%;
    transform: translateX(-50%);
    width: 60px;
    height: 3px;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    border-radius: var(--radius-sm);
}

/* Form Styles */
.date-form {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

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

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

.form-group--half {
    flex: 1;
}

.form-label {
    font-weight: 600;
    color: var(--text-primary);
    font-size: var(--font-size-sm);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.form-input,
.form-select {
    padding: var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
    background-color: var(--input-background);
    color: var(--text-primary);
    transition: all var(--transition-normal);
    outline: none;
}

.form-input:focus,
.form-select:focus {
    border-color: var(--secondary-color);
    box-shadow: 0 0 0 3px rgba(78, 205, 196, 0.1);
    transform: translateY(-1px);
}

.form-input:invalid {
    border-color: var(--accent-color);
}

.form-help {
    font-size: var(--font-size-xs);
    color: var(--text-muted);
    font-style: italic;
}

/* Button Styles */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-xl);
    border: none;
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
    font-weight: 600;
    text-decoration: none;
    cursor: pointer;
    transition: all var(--transition-normal);
    position: relative;
    overflow: hidden;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.2), transparent);
    transition: left var(--transition-slow);
}

.btn:hover::before {
    left: 100%;
}

.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: linear-gradient(135deg, var(--accent-color), var(--warning-color));
    color: white;
    box-shadow: var(--shadow-md);
}

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

.btn__icon {
    font-size: var(--font-size-lg);
}

/* Results Styles */
.results {
    margin-top: var(--spacing-xl);
    padding: var(--spacing-xl);
    background: linear-gradient(135deg, rgba(78, 205, 196, 0.1), rgba(26, 83, 92, 0.1));
    border-radius: var(--radius-lg);
    border: 2px solid var(--border-color);
    animation: fadeInUp 0.5s ease-out;
}

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

.results__title {
    font-size: var(--font-size-xl);
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-lg);
    text-align: center;
}

.results__grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.result-item {
    text-align: center;
    padding: var(--spacing-md);
    background: var(--card-background);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-sm);
    transition: transform var(--transition-normal);
}

.result-item:hover {
    transform: scale(1.05);
}

.result-item__value {
    display: block;
    font-size: var(--font-size-2xl);
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: var(--spacing-xs);
}

.result-item__label {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.results__detailed {
    padding: var(--spacing-md);
    background: var(--card-background);
    border-radius: var(--radius-md);
    font-size: var(--font-size-lg);
    text-align: center;
    color: var(--text-secondary);
    font-weight: 500;
}

.new-date-result {
    text-align: center;
    padding: var(--spacing-xl);
    background: var(--card-background);
    border-radius: var(--radius-md);
    font-size: var(--font-size-2xl);
    font-weight: 600;
    color: var(--primary-color);
    box-shadow: var(--shadow-sm);
}

/* Info Section */
.info-section {
    margin-top: var(--spacing-2xl);
}

.info-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-xl);
    margin-top: var(--spacing-xl);
}

.info-item {
    text-align: center;
    padding: var(--spacing-xl);
    background: linear-gradient(135deg, rgba(78, 205, 196, 0.05), rgba(26, 83, 92, 0.05));
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-color);
    transition: transform var(--transition-normal);
}

.info-item:hover {
    transform: translateY(-5px);
}

.info-item__icon {
    font-size: var(--font-size-3xl);
    margin-bottom: var(--spacing-md);
    display: block;
}

.info-item h3 {
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
}

.info-item p {
    color: var(--text-secondary);
    line-height: 1.6;
}

/* Message Styles */
.error-message,
.success-message {
    position: fixed;
    top: 20px;
    right: 20px;
    z-index: 1000;
    max-width: 400px;
    animation: slideInRight 0.3s ease-out;
}

@keyframes slideInRight {
    from {
        transform: translateX(100%);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}

.error-message__content,
.success-message__content {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-md) var(--spacing-lg);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    backdrop-filter: blur(10px);
}

.error-message__content {
    background: rgba(255, 107, 107, 0.95);
    color: white;
    border: 1px solid var(--accent-color);
}

.success-message__content {
    background: rgba(78, 205, 196, 0.95);
    color: white;
    border: 1px solid var(--secondary-color);
}

.error-message__icon,
.success-message__icon {
    font-size: var(--font-size-lg);
    flex-shrink: 0;
}

.error-message__text,
.success-message__text {
    flex: 1;
    font-weight: 500;
}

.error-message__close,
.success-message__close {
    background: none;
    border: none;
    color: white;
    font-size: var(--font-size-xl);
    cursor: pointer;
    padding: 0;
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    transition: background-color var(--transition-fast);
}

.error-message__close:hover,
.success-message__close:hover {
    background: rgba(255, 255, 255, 0.2);
}

/* Loading Indicator */
.loading {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
    backdrop-filter: blur(5px);
}

.loading__spinner {
    width: 50px;
    height: 50px;
    border: 4px solid rgba(78, 205, 196, 0.3);
    border-top: 4px solid var(--secondary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Footer */
.footer {
    background: var(--primary-color);
    color: white;
    padding: var(--spacing-lg) 0;
    margin-top: auto;
    text-align: center;
}

.footer__content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

.footer__text {
    font-size: var(--font-size-sm);
    margin: 0;
}

.footer__link {
    color: var(--secondary-color);
    text-decoration: none;
    font-weight: 600;
    transition: color var(--transition-normal);
}

.footer__link:hover {
    color: white;
    text-decoration: underline;
}

/* Responsive Design */
@media (max-width: 768px) {
    .header__title {
        font-size: var(--font-size-xl);
        text-align: center;
    }
    
    .header__content {
        flex-direction: column;
        gap: var(--spacing-md);
    }
    
    .theme-toggle {
        position: absolute;
        top: var(--spacing-md);
        right: var(--spacing-md);
    }
    
    .container {
        padding: 0 var(--spacing-sm);
    }
    
    .card {
        padding: var(--spacing-lg);
    }
    
    .form-row {
        grid-template-columns: 1fr;
    }
    
    .results__grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .info-grid {
        grid-template-columns: 1fr;
    }
    
    .error-message,
    .success-message {
        top: 10px;
        right: 10px;
        left: 10px;
        max-width: none;
    }
}

@media (max-width: 480px) {
    .header__title {
        font-size: var(--font-size-lg);
    }
    
    .header__icon {
        font-size: var(--font-size-xl);
    }
    
    .card__title {
        font-size: var(--font-size-xl);
    }
    
    .results__grid {
        grid-template-columns: 1fr;
    }
    
    .result-item__value {
        font-size: var(--font-size-xl);
    }
    
    .new-date-result {
        font-size: var(--font-size-xl);
    }
}

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

/* Focus Styles for Accessibility */
.btn:focus,
.form-input:focus,
.form-select:focus,
.theme-toggle:focus {
    outline: 2px solid var(--secondary-color);
    outline-offset: 2px;
}

/* High Contrast Mode Support */
@media (prefers-contrast: high) {
    :root {
        --border-color: #000000;
        --shadow-color: rgba(0, 0, 0, 0.5);
    }
    
    .card {
        border-width: 2px;
    }
    
    .btn {
        border: 2px solid currentColor;
    }
}

/* Print Styles */
@media print {
    .header,
    .footer,
    .theme-toggle,
    .error-message,
    .success-message,
    .loading {
        display: none !important;
    }
    
    .card {
        box-shadow: none;
        border: 1px solid #000;
    }
    
    .main {
        padding: 0;
    }
}