/* CSS Variables & Theme Setup */
.heart-rate-calculator-container {
    /* Light Mode Variables */
    --bg-primary: #f5f5f0;
    --bg-secondary: #fff;
    --bg-section: #fff;
    --border-color: #333;
    --text-primary: #222;
    --text-secondary: #555;
    --text-light: #666;
    
    /* Colors */
    --color-accent: #3498db;     /* Blue */
    --color-success: #27ae60;    /* Green */
    --color-warning: #f39c12;    /* Orange */
    --color-danger: #e74c3c;     /* Red */
    --color-purple: #9b59b6;     /* Purple */
    
    /* Zone Colors */
    --zone-1: #95a5a6; /* Gray - Warm up */
    --zone-2: #3498db; /* Blue - Fat burn */
    --zone-3: #27ae60; /* Green - Cardio */
    --zone-4: #f39c12; /* Orange - Hard */
    --zone-5: #e74c3c; /* Red - Max */

    /* Shadows & Radius */
    --shadow-sm: 2px 2px 0 rgba(0,0,0,0.1);
    --shadow-md: 4px 4px 0 rgba(0,0,0,0.15);
    --shadow-lg: 8px 8px 0 rgba(0,0,0,0.15);
    --radius-container: 8px;
    --radius-section: 6px;
    --radius-button: 4px;
    --radius-input: 4px;
    
    --input-focus-bg: #fffacd;
    --copy-btn-bg: #fff;
    --copy-btn-hover-bg: #f0f0f0;
}

/* Dark Mode Variables */
.heart-rate-calculator-container.dark {
    --bg-primary: #1a1a1a;
    --bg-secondary: #2d2d2d;
    --bg-section: #2d2d2d;
    --border-color: #e0e0e0;
    --text-primary: #e8e8e8;
    --text-secondary: #b0b0b0;
    --text-light: #909090;
    
    --color-accent: #5dade2;
    --color-success: #52c77a;
    --color-warning: #f5b041;
    --color-danger: #ec7063;
    --color-purple: #af7ac5;
    
    /* Brighter Zone Colors for Dark Mode */
    --zone-1: #bdc3c7;
    --zone-2: #5dade2;
    --zone-3: #52c77a;
    --zone-4: #f5b041;
    --zone-5: #ec7063;

    --shadow-sm: 2px 2px 0 rgba(255,255,255,0.08);
    --shadow-md: 4px 4px 0 rgba(255,255,255,0.12);
    --shadow-lg: 8px 8px 0 rgba(255,255,255,0.12);
    
    --input-focus-bg: #3a3a3a;
    --copy-btn-bg: #3a3a3a;
    --copy-btn-hover-bg: #4a4a4a;
}

/* System Dark Mode Auto-Detection */
@media (prefers-color-scheme: dark) {
    .heart-rate-calculator-container:not(.dark):not(.light) {
        --bg-primary: #1a1a1a;
        --bg-secondary: #2d2d2d;
        --bg-section: #2d2d2d;
        --border-color: #e0e0e0;
        --text-primary: #e8e8e8;
        --text-secondary: #b0b0b0;
        --text-light: #909090;
        --color-accent: #5dade2;
        --color-success: #52c77a;
        --color-warning: #f5b041;
        --color-danger: #ec7063;
        --color-purple: #af7ac5;
        --zone-1: #bdc3c7;
        --zone-2: #5dade2;
        --zone-3: #52c77a;
        --zone-4: #f5b041;
        --zone-5: #ec7063;
        --shadow-sm: 2px 2px 0 rgba(255,255,255,0.08);
        --shadow-md: 4px 4px 0 rgba(255,255,255,0.12);
        --shadow-lg: 8px 8px 0 rgba(255,255,255,0.12);
        --input-focus-bg: #3a3a3a;
        --copy-btn-bg: #3a3a3a;
        --copy-btn-hover-bg: #4a4a4a;
    }
}

/* Global Styles */
.heart-rate-calculator-container,
.heart-rate-calculator-container * {
    box-sizing: border-box;
}

.heart-rate-calculator-container {
    position: relative;
    max-width: 900px;
    width: 100%;
    margin: 8px auto;
    padding: 8px;
    background: var(--bg-primary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-container);
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Malgun Gothic', sans-serif;
    color: var(--text-primary);
    box-shadow: var(--shadow-lg);
    line-height: 1.5;
}

/* Header */
.header {
    margin-bottom: 12px;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border-color);
}

.main-title {
    margin: 0 0 4px 0;
    font-size: 24px; /* Tablet size base */
    font-weight: 800;
    color: var(--text-primary);
}

.subtitle {
    margin: 0;
    font-size: 16px;
    color: var(--text-secondary);
}

/* Dark Mode Toggle - Specific Request: Radius 8px */
.dark-mode-toggle {
    position: absolute;
    top: 10px;
    right: 10px;
    padding: 6px 10px;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 8px !important; /* ⭐ Requested 8px */
    cursor: pointer;
    transition: all 0.2s;
    box-shadow: 2px 2px 0 rgba(0,0,0,0.15);
    font-size: 17.5px;
    z-index: 10;
}

.dark-mode-toggle:hover {
    transform: translate(0.5px, 0.5px);
    box-shadow: 1.5px 1.5px 0 rgba(0,0,0,0.15);
}

.dark-mode-toggle:active {
    transform: translate(2px, 2px);
    box-shadow: none;
}

/* Layout: 2-Column Grid */
.main-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 8px;
}

/* Sections */
.input-section,
.result-section {
    background: var(--bg-section);
    padding: 8px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-section);
    box-shadow: var(--shadow-md);
}

.section-header {
    display: flex;
    align-items: center;
    gap: 6px;
    margin-bottom: 8px;
    padding-bottom: 6px;
    border-bottom: 1px solid var(--border-color);
    font-size: 17px;
    font-weight: 600;
    color: var(--text-primary);
}

/* Input Fields */
.input-group {
    margin-bottom: 12px;
}

.input-group label {
    display: block;
    margin-bottom: 5px;
    font-size: 16px;
    font-weight: 500;
    color: var(--text-primary);
}

.input-group input,
.input-group select {
    width: 100%;
    padding: 7px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-input);
    background: var(--bg-secondary);
    color: var(--text-primary);
    font-size: 18px;
    font-family: inherit;
    transition: all 0.2s;
    box-shadow: var(--shadow-sm);
}

.numeric-input {
    font-family: 'Courier New', monospace;
    font-weight: 700;
}

.input-group input:focus,
.input-group select:focus {
    outline: none;
    border-color: var(--color-accent);
    background: var(--input-focus-bg);
}

.input-description {
    margin-top: 4px;
    font-size: 14.5px;
    color: var(--text-light);
}

.hidden {
    display: none;
}

/* Buttons */
.calculate-btn {
    width: 100%;
    padding: 10px 16px;
    margin-top: 8px;
    background: var(--color-accent);
    color: #fff;
    border: 1.5px solid var(--border-color);
    border-radius: var(--radius-button);
    font-size: 18px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.15s;
    box-shadow: 4px 4px 0 rgba(0,0,0,0.2);
}

.calculate-btn:hover {
    filter: brightness(1.05);
    transform: translate(1px, 1px);
    box-shadow: 3px 3px 0 rgba(0,0,0,0.2);
}

.calculate-btn:active {
    transform: translate(4px, 4px);
    box-shadow: none;
}

.button-group {
    display: flex;
    gap: 6px;
    margin-top: 10px;
}

.sample-btn,
.reset-btn {
    flex: 1;
    padding: 8px 12px;
    font-size: 16px;
    font-weight: 500;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-button);
    cursor: pointer;
    transition: all 0.15s;
    box-shadow: 2px 2px 0 rgba(0,0,0,0.2);
    color: #fff;
}

.sample-btn { background: var(--color-success); }
.reset-btn { background: var(--color-warning); }

.sample-btn:active,
.reset-btn:active {
    transform: translate(2px, 2px);
    box-shadow: none;
}

/* Results */
.result-item {
    padding: 10px;
    margin-bottom: 12px;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-button);
    box-shadow: var(--shadow-sm);
    text-align: center;
}

.result-label {
    display: block;
    font-size: 15.5px;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: 4px;
}

.result-value {
    display: block;
    font-size: 22px;
    font-weight: 700;
    color: var(--text-primary);
    font-family: 'Courier New', monospace;
}

.result-value.highlight {
    font-size: 26px;
    color: var(--color-accent);
}

/* Chart */
.chart-container {
    position: relative;
    height: 200px;
    width: 100%;
    margin-bottom: 15px;
}

/* Zone Table */
.zone-table-container {
    overflow-x: auto;
    margin-bottom: 15px;
}

.zone-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 15px;
    text-align: left;
}

.zone-table th,
.zone-table td {
    padding: 8px;
    border-bottom: 1px solid var(--border-color);
    color: var(--text-primary);
}

.zone-table th {
    font-weight: 600;
    background-color: rgba(0,0,0,0.05);
}

/* Zone Tags */
.zone-tag {
    display: inline-block;
    padding: 2px 6px;
    border-radius: 4px;
    color: #fff;
    font-weight: 600;
    font-size: 13px;
    text-shadow: 0 1px 1px rgba(0,0,0,0.3);
}

/* Image Save Button & Watermark */
.save-image-btn {
    width: 100%;
    padding: 8px 16px;
    background: var(--color-purple);
    color: #fff;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-button);
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    box-shadow: 2px 2px 0 rgba(0,0,0,0.2);
}

.save-image-btn.capturing {
    display: none;
}

.watermark {
    position: absolute;
    bottom: 10px;
    right: 10px;
    font-size: 13px;
    font-weight: 500;
    color: var(--text-light);
    opacity: 0.6;
    pointer-events: none;
}

/* Toast */
.toast {
    position: fixed;
    bottom: 20px;
    right: 20px;
    padding: 10px 16px;
    background: var(--text-primary);
    color: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-button);
    font-size: 16px;
    font-weight: 500;
    box-shadow: 4px 4px 0 rgba(0,0,0,0.3);
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transition: all 0.3s;
}

.toast.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(-5px);
}

.toast.success { background: var(--color-success); color: #fff; }
.toast.error { background: var(--color-danger); color: #fff; }

/* Responsive */
@media (max-width: 768px) {
    .heart-rate-calculator-container {
        margin: 6px 5px;
        padding: 7px;
        width: calc(100% - 10px);
    }
    .main-grid {
        grid-template-columns: 1fr;
        gap: 6px;
    }
    .main-title { font-size: 28px; } /* Desktop title size restore logic if needed, but 24px is safer */
}

@media (min-width: 769px) {
    .main-title { font-size: 28px; }
}