/* 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-red: #FF6B6B;
    --accent-yellow: #FFE66D;
    
    /* Typography */
    --font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    --font-size-base: 16px;
    --font-size-small: 14px;
    --font-size-large: 18px;
    --font-size-xl: 24px;
    --font-size-xxl: 32px;
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-xxl: 3rem;
    
    /* Border Radius */
    --border-radius-sm: 4px;
    --border-radius-md: 8px;
    --border-radius-lg: 12px;
    
    /* Shadows */
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.15);
    
    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

/* Base Styles */
html {
    font-size: var(--font-size-base);
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    line-height: 1.6;
    color: var(--primary-color);
    background-color: var(--background-color);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

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

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

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

.header__icon {
    font-size: var(--font-size-xxl);
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.1); }
}

.header__subtitle {
    font-size: var(--font-size-large);
    opacity: 0.9;
    font-weight: 300;
}

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

/* Calculator Section */
.calculator {
    margin-bottom: var(--spacing-xxl);
}

.calculator__card {
    background: white;
    border-radius: var(--border-radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-lg);
    max-width: 600px;
    margin: 0 auto;
}

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

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

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

.form-group__label {
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    color: var(--primary-color);
}

.form-group__required {
    color: var(--accent-red);
}

.form-group__input,
.form-group__select {
    padding: var(--spacing-md);
    border: 2px solid #e1e5e9;
    border-radius: var(--border-radius-md);
    font-size: var(--font-size-base);
    transition: var(--transition-fast);
    background-color: white;
}

.form-group__input:focus,
.form-group__select:focus {
    outline: none;
    border-color: var(--secondary-color);
    box-shadow: 0 0 0 3px rgba(78, 205, 196, 0.1);
}

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

.form-group__help {
    margin-top: var(--spacing-xs);
    color: #6c757d;
    font-size: var(--font-size-small);
}

/* Button Styles */
.btn {
    padding: var(--spacing-md) var(--spacing-xl);
    border: none;
    border-radius: var(--border-radius-md);
    font-size: var(--font-size-base);
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition-fast);
    text-decoration: none;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
}

.btn--primary {
    background-color: var(--primary-color);
    color: white;
}

.btn--primary:hover {
    background-color: #0f3c42;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn--secondary {
    background-color: var(--secondary-color);
    color: white;
}

.btn--secondary:hover {
    background-color: #3bb5ad;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn--outline {
    background-color: transparent;
    color: var(--primary-color);
    border: 2px solid var(--primary-color);
}

.btn--outline:hover {
    background-color: var(--primary-color);
    color: white;
}

.btn--small {
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: var(--font-size-small);
}

/* Error Message */
.error-message {
    background-color: #ffeaea;
    color: var(--accent-red);
    padding: var(--spacing-md);
    border-radius: var(--border-radius-md);
    border-left: 4px solid var(--accent-red);
    margin-top: var(--spacing-lg);
    display: none;
}

.error-message.show {
    display: block;
    animation: slideIn 0.3s ease;
}

@keyframes slideIn {
    from { opacity: 0; transform: translateY(-10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Results Section */
.results {
    margin-bottom: var(--spacing-xxl);
}

.results__card {
    background: white;
    border-radius: var(--border-radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-lg);
    max-width: 800px;
    margin: 0 auto;
}

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

/* Results Summary */
.results__summary {
    background-color: #f8f9fa;
    padding: var(--spacing-lg);
    border-radius: var(--border-radius-md);
    margin-bottom: var(--spacing-xl);
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-md);
}

.summary-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.summary-item__label {
    font-weight: 600;
    color: var(--primary-color);
}

.summary-item__value {
    font-weight: 700;
    color: var(--secondary-color);
}

/* Heart Rate Zones */
.zones {
    margin-bottom: var(--spacing-xl);
}

.zone {
    background: white;
    border-radius: var(--border-radius-md);
    padding: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
    box-shadow: var(--shadow-sm);
    border-left: 4px solid var(--secondary-color);
    transition: var(--transition-fast);
}

.zone:hover {
    transform: translateX(4px);
    box-shadow: var(--shadow-md);
}

.zone--active {
    border-left-color: var(--accent-yellow);
    background-color: #fffef0;
}

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

.zone__name {
    font-size: var(--font-size-large);
    font-weight: 700;
    color: var(--primary-color);
}

.zone__range {
    font-size: var(--font-size-large);
    font-weight: 600;
    color: var(--secondary-color);
}

.zone__description {
    color: #6c757d;
    margin-bottom: var(--spacing-md);
}

.zone__bar {
    height: 8px;
    background-color: #e9ecef;
    border-radius: 4px;
    overflow: hidden;
    position: relative;
}

.zone__progress {
    height: 100%;
    background: linear-gradient(90deg, var(--secondary-color), var(--accent-yellow));
    border-radius: 4px;
    transition: width 1s ease;
}

/* Results Actions */
.results__actions {
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
    flex-wrap: wrap;
}

/* Saved Data Section */
.saved-data {
    margin-bottom: var(--spacing-xxl);
}

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

.saved-data__title {
    font-size: var(--font-size-xl);
    color: var(--primary-color);
}

.saved-data__list {
    display: grid;
    gap: var(--spacing-md);
}

.saved-item {
    background: white;
    padding: var(--spacing-lg);
    border-radius: var(--border-radius-md);
    box-shadow: var(--shadow-sm);
    border-left: 4px solid var(--secondary-color);
}

.saved-item__header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-sm);
}

.saved-item__date {
    font-size: var(--font-size-small);
    color: #6c757d;
}

.saved-item__delete {
    background: none;
    border: none;
    color: var(--accent-red);
    cursor: pointer;
    padding: var(--spacing-xs);
    border-radius: var(--border-radius-sm);
    transition: var(--transition-fast);
}

.saved-item__delete:hover {
    background-color: #ffeaea;
}

.saved-item__info {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-sm);
    font-size: var(--font-size-small);
}

/* FAQ Section */
.faq {
    margin-bottom: var(--spacing-xxl);
}

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

.faq__item {
    background: white;
    border-radius: var(--border-radius-md);
    margin-bottom: var(--spacing-md);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
}

.faq__question {
    width: 100%;
    padding: var(--spacing-lg);
    background: none;
    border: none;
    text-align: left;
    font-size: var(--font-size-base);
    font-weight: 600;
    color: var(--primary-color);
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: var(--transition-fast);
}

.faq__question:hover {
    background-color: #f8f9fa;
}

.faq__question[aria-expanded="true"] .faq__icon {
    transform: rotate(45deg);
}

.faq__icon {
    font-size: var(--font-size-large);
    transition: var(--transition-fast);
}

.faq__answer {
    padding: 0 var(--spacing-lg) var(--spacing-lg);
    color: #6c757d;
    display: none;
    animation: fadeIn 0.3s ease;
}

.faq__answer.show {
    display: block;
}

.faq__answer ul {
    margin: var(--spacing-md) 0;
    padding-left: var(--spacing-lg);
}

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

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

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

.footer__text {
    font-size: var(--font-size-small);
    opacity: 0.8;
}

/* Loading Indicator */
.loading {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(255, 255, 255, 0.9);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.loading__spinner {
    width: 40px;
    height: 40px;
    border: 4px solid #f3f3f3;
    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); }
}

/* Toast Notifications */
.toast {
    position: fixed;
    bottom: var(--spacing-lg);
    right: var(--spacing-lg);
    background-color: var(--primary-color);
    color: white;
    padding: var(--spacing-md) var(--spacing-lg);
    border-radius: var(--border-radius-md);
    box-shadow: var(--shadow-lg);
    transform: translateX(100%);
    transition: var(--transition-normal);
    z-index: 1000;
}

.toast.show {
    transform: translateX(0);
}

.toast--success {
    background-color: #28a745;
}

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

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 0 var(--spacing-sm);
    }
    
    .header__title {
        font-size: var(--font-size-xl);
    }
    
    .calculator__card,
    .results__card {
        padding: var(--spacing-lg);
    }
    
    .results__summary {
        grid-template-columns: 1fr;
    }
    
    .summary-item {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-xs);
    }
    
    .zone__header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-xs);
    }
    
    .results__actions {
        flex-direction: column;
    }
    
    .saved-data__header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-md);
    }
    
    .saved-item__header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-sm);
    }
    
    .saved-item__info {
        grid-template-columns: 1fr;
    }
    
    .toast {
        right: var(--spacing-sm);
        left: var(--spacing-sm);
    }
}

@media (max-width: 480px) {
    .header {
        padding: var(--spacing-lg) 0;
    }
    
    .header__title {
        font-size: var(--font-size-large);
        flex-direction: column;
        gap: var(--spacing-xs);
    }
    
    .main {
        padding: var(--spacing-lg) 0;
    }
    
    .calculator__card,
    .results__card {
        padding: var(--spacing-md);
    }
    
    .btn {
        width: 100%;
    }
}

/* Print Styles */
@media print {
    .header,
    .footer,
    .calculator,
    .saved-data,
    .faq {
        display: none;
    }
    
    .results {
        box-shadow: none;
    }
    
    .results__card {
        box-shadow: none;
        border: 1px solid #ddd;
    }
}

/* High Contrast Mode */
@media (prefers-contrast: high) {
    :root {
        --primary-color: #000000;
        --secondary-color: #0066cc;
        --background-color: #ffffff;
    }
}

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