:root {
    --primary-color: #2196F3;
    --success-color: #4CAF50;
    --warning-color: #FFC107;
    --danger-color: #F44336;
    --purple-color: #9C27B0;
    --background-color: #f5f5f5;
    --surface-color: #ffffff;
    --text-primary: #333333;
    --text-secondary: #666666;
    --border-color: #e0e0e0;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 4px 16px rgba(0, 0, 0, 0.15);
    --border-radius: 12px;
    --transition: all 0.3s ease;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    background-color: var(--background-color);
    color: var(--text-primary);
    line-height: 1.6;
    padding-bottom: 120px; /* Increased to account for footer */
}

/* Header */
.app-header {
    background: linear-gradient(135deg, var(--primary-color), var(--purple-color));
    color: white;
    padding: 1rem;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow-lg);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 1200px;
    margin: 0 auto;
}

.app-header h1 {
    font-size: 1.5rem;
    font-weight: 600;
}

.header-actions {
    display: flex;
    gap: 0.5rem;
}

.language-btn, .settings-btn {
    background: rgba(255, 255, 255, 0.2);
    border: none;
    color: white;
    padding: 0.5rem;
    border-radius: 8px;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 0.25rem;
    font-size: 0.9rem;
}

.language-btn:hover, .settings-btn:hover {
    background: rgba(255, 255, 255, 0.3);
}

/* Main Content */
.app-main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem;
}

.content-section {
    display: none;
    animation: fadeIn 0.3s ease;
}

.content-section.active {
    display: block;
}

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

/* Battery Status Card */
.battery-status-card {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    padding: 2rem;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow);
    text-align: center;
}

.battery-visual {
    display: flex;
    flex-direction: column;
    align-items: center;
    margin-bottom: 2rem;
}

.battery-container {
    position: relative;
    width: 120px;
    height: 60px;
    border: 3px solid var(--border-color);
    border-radius: 8px;
    margin-bottom: 1rem;
    background: #f9f9f9;
}

.battery-container::after {
    content: '';
    position: absolute;
    right: -8px;
    top: 50%;
    transform: translateY(-50%);
    width: 5px;
    height: 20px;
    background: var(--border-color);
    border-radius: 0 2px 2px 0;
}

.battery-level {
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    background: linear-gradient(90deg, var(--success-color), var(--primary-color));
    border-radius: 4px;
    transition: var(--transition);
    width: 0%;
}

.battery-level.low {
    background: var(--danger-color);
}

.battery-level.medium {
    background: var(--warning-color);
}

.battery-percentage {
    font-size: 2rem;
    font-weight: bold;
    color: var(--primary-color);
}

.battery-info {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1rem;
    text-align: left;
    max-width: 400px;
    margin: 0 auto;
}

.info-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.5rem 0;
    border-bottom: 1px solid var(--border-color);
}

.info-label {
    font-weight: 500;
    color: var(--text-secondary);
}

.info-value {
    font-weight: 600;
    color: var(--text-primary);
}

.health-good { color: var(--success-color); }
.health-fair { color: var(--warning-color); }
.health-poor { color: var(--danger-color); }

/* Quick Actions */
.quick-actions {
    display: flex;
    gap: 1rem;
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
}

.action-btn {
    flex: 1;
    min-width: 150px;
    padding: 1rem;
    border: none;
    border-radius: var(--border-radius);
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}

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

.action-btn.secondary {
    background: var(--surface-color);
    color: var(--primary-color);
    border: 2px solid var(--primary-color);
}

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

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

/* Alerts */
.alerts-container {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.alert {
    padding: 1rem;
    border-radius: var(--border-radius);
    border-left: 4px solid;
    animation: slideIn 0.3s ease;
}

.alert.warning {
    background: #fff8e1;
    border-color: var(--warning-color);
    color: #f57f17;
}

.alert.danger {
    background: #ffebee;
    border-color: var(--danger-color);
    color: #c62828;
}

.alert.info {
    background: #e3f2fd;
    border-color: var(--primary-color);
    color: #1565c0;
}

@keyframes slideIn {
    from { opacity: 0; transform: translateX(-20px); }
    to { opacity: 1; transform: translateX(0); }
}

/* Section Headers */
.section-header {
    margin-bottom: 1.5rem;
    text-align: center;
}

.section-header h2 {
    font-size: 1.8rem;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
}

/* Stats Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 1rem;
    margin-bottom: 2rem;
}

.stat-card {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    text-align: center;
    box-shadow: var(--shadow);
    transition: var(--transition);
}

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

.stat-icon {
    font-size: 2rem;
    margin-bottom: 0.5rem;
}

.stat-value {
    font-size: 1.5rem;
    font-weight: bold;
    color: var(--primary-color);
    margin-bottom: 0.25rem;
}

.stat-label {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

/* Chart Container */
.chart-container {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-bottom: 2rem;
    box-shadow: var(--shadow);
}

#battery-chart {
    width: 100%;
    max-width: 100%;
    height: auto;
}

/* Readings History */
.readings-history h3 {
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.readings-list {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    max-height: 300px;
    overflow-y: auto;
}

.reading-item {
    padding: 1rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

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

.reading-info {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.reading-level {
    font-weight: 600;
    font-size: 1.1rem;
}

.reading-time {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.reading-status {
    padding: 0.25rem 0.5rem;
    border-radius: 4px;
    font-size: 0.8rem;
    font-weight: 500;
}

.reading-status.charging {
    background: #e8f5e8;
    color: var(--success-color);
}

.reading-status.discharging {
    background: #fff3e0;
    color: var(--warning-color);
}

/* Optimization Tips */
.optimization-tips {
    margin-bottom: 2rem;
}

.tip-card {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-bottom: 1rem;
    box-shadow: var(--shadow);
    border-left: 4px solid var(--primary-color);
}

.tip-header {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
}

.tip-icon {
    font-size: 1.2rem;
}

.tip-title {
    font-weight: 600;
    color: var(--text-primary);
}

.tip-description {
    color: var(--text-secondary);
    line-height: 1.5;
}

/* Charging Habits */
.charging-habits h3 {
    margin-bottom: 1rem;
    color: var(--text-primary);
}

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

.habit-card {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
    display: flex;
    align-items: center;
    gap: 1rem;
    transition: var(--transition);
}

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

.habit-icon {
    font-size: 2rem;
    flex-shrink: 0;
}

.habit-content h4 {
    color: var(--text-primary);
    margin-bottom: 0.5rem;
}

.habit-content p {
    color: var(--text-secondary);
    font-size: 0.9rem;
    line-height: 1.4;
}

/* Settings */
.settings-group {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow);
}

.settings-group h3 {
    margin-bottom: 1rem;
    color: var(--text-primary);
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 0.5rem;
}

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

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

.setting-label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
    flex: 1;
}

.setting-label input[type="checkbox"] {
    width: 20px;
    height: 20px;
    accent-color: var(--primary-color);
    cursor: pointer;
}

.setting-label input[type="number"] {
    padding: 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    width: 80px;
}

.settings-actions {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
}

/* FAQ */
.faq-container {
    background: var(--surface-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    overflow: hidden;
}

.faq-item {
    border-bottom: 1px solid var(--border-color);
}

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

.faq-question {
    width: 100%;
    padding: 1.5rem;
    background: none;
    border: none;
    text-align: left;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 1rem;
    font-weight: 500;
    color: var(--text-primary);
    transition: var(--transition);
}

.faq-question:hover {
    background: #f8f9fa;
}

.faq-question[aria-expanded="true"] {
    background: #f0f7ff;
    color: var(--primary-color);
}

.faq-icon {
    font-size: 1.2rem;
    font-weight: bold;
    transition: var(--transition);
}

.faq-question[aria-expanded="true"] .faq-icon {
    transform: rotate(45deg);
}

.faq-answer {
    padding: 0 1.5rem 1.5rem;
    color: var(--text-secondary);
    line-height: 1.6;
    animation: fadeIn 0.3s ease;
}

/* Bottom Navigation */
.bottom-nav {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background: var(--surface-color);
    border-top: 1px solid var(--border-color);
    display: flex;
    justify-content: space-around;
    padding: 0.5rem 0;
    z-index: 100;
    box-shadow: 0 -2px 8px rgba(0, 0, 0, 0.1);
}

/* Ensure footer appears above bottom navigation */

.nav-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 0.5rem;
    color: var(--text-secondary);
    text-decoration: none;
    transition: var(--transition);
    flex: 1;
    max-width: 80px;
}

.nav-item i {
    font-size: 1.2rem;
    margin-bottom: 0.25rem;
}

.nav-item span {
    font-size: 0.75rem;
    font-weight: 500;
}

.nav-item.active,
.nav-item:hover {
    color: var(--primary-color);
}

/* Footer */
footer {
    text-align: center;
    padding: 2rem 1rem;
    color: var(--text-secondary);
    font-size: 0.9rem;
    background: var(--surface-color);
    border-top: 1px solid var(--border-color);
    margin-top: 2rem;
    position: relative;
    z-index: 1;
}

footer a {
    color: var(--primary-color);
    text-decoration: none;
    transition: var(--transition);
}

footer a:hover {
    color: var(--purple-color);
    text-decoration: underline;
}

/* Responsive Design */
@media (max-width: 768px) {
    .app-main {
        padding: 0.5rem;
    }
    
    .battery-status-card {
        padding: 1.5rem;
    }
    
    .battery-container {
        width: 100px;
        height: 50px;
    }
    
    .battery-percentage {
        font-size: 1.5rem;
    }
    
    .quick-actions {
        flex-direction: column;
    }
    
    .action-btn {
        min-width: auto;
    }
    
    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 0.5rem;
    }
    
    .stat-card {
        padding: 1rem;
    }
    
    .habits-grid {
        grid-template-columns: 1fr;
    }
    
    .settings-actions {
        flex-direction: column;
    }
    
    .header-content h1 {
        font-size: 1.2rem;
    }
    
    /* Ensure footer is visible on mobile */
    footer {
        padding: 1rem 0.5rem;
        font-size: 0.8rem;
        margin-top: 1rem;
    }
    
    body {
        padding-bottom: 100px;
    }
}

@media (max-width: 480px) {
    .stats-grid {
        grid-template-columns: 1fr;
    }
    
    .habit-card {
        flex-direction: column;
        text-align: center;
    }
    
    .faq-question {
        padding: 1rem;
        font-size: 0.9rem;
    }
    
    .faq-answer {
        padding: 0 1rem 1rem;
    }
}

/* Utility Classes */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }
.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }

/* Loading Animation */
.loading {
    display: inline-block;
    width: 20px;
    height: 20px;
    border: 3px solid rgba(33, 150, 243, 0.3);
    border-radius: 50%;
    border-top-color: var(--primary-color);
    animation: spin 1s ease-in-out infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Smooth transitions for all interactive elements */
button, a, .nav-item, .faq-question, .stat-card, .habit-card {
    transition: var(--transition);
}

/* Focus states for accessibility */
button:focus, a:focus, input:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* Hide scrollbar but keep functionality */
.readings-list::-webkit-scrollbar {
    width: 6px;
}

.readings-list::-webkit-scrollbar-track {
    background: #f1f1f1;
    border-radius: 3px;
}

.readings-list::-webkit-scrollbar-thumb {
    background: var(--primary-color);
    border-radius: 3px;
}

.readings-list::-webkit-scrollbar-thumb:hover {
    background: #1976D2;
}