:root {
    --primary: #EF4444;
    --primary-hover: #DC2626;
    --secondary: #F87171;
    --accent: #FCA5A5;

    --bg-dark: #1A0D0D;
    --panel-bg: rgba(35, 15, 15, 0.6);
    --glass-bg: rgba(45, 20, 20, 0.4);
    --glass-border: rgba(248, 113, 113, 0.15);

    --text-main: #FEF2F2;
    --text-muted: #FECACA;

    --zone-rest: #60A5FA;
    --zone-fat: #34D399;
    --zone-cardio: #FBBF24;
    --zone-peak: #EF4444;

    --font-sans: 'Inter', system-ui, sans-serif;
    --font-mono: 'JetBrains Mono', monospace;

    --radius: 16px;
    --radius-sm: 8px;
    --radius-pill: 99px;

    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: var(--font-sans);
    background: var(--bg-dark);
    color: var(--text-main);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    padding: 1.5rem;
    background-image:
        radial-gradient(circle at 10% 20%, rgba(239, 68, 68, 0.08), transparent 40%),
        radial-gradient(circle at 90% 80%, rgba(248, 113, 113, 0.05), transparent 40%);
}

.hidden {
    display: none !important;
}

.app-container {
    width: 100%;
    max-width: 1000px;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

/* Glass & Panels */
.glass {
    background: var(--glass-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--glass-border);
}

.glass-panel {
    background: var(--panel-bg);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--glass-border);
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
    border-radius: var(--radius);
    padding: 1.5rem;
}

/* Header */
.top-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 1.5rem;
    border-radius: var(--radius);
}

.brand {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.brand h1 {
    font-size: 1.25rem;
    font-weight: 700;
    letter-spacing: -0.02em;
}

.pulse-ring {
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
}

.pulse-ring::before {
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    background: var(--primary);
    border-radius: 50%;
    opacity: 0.3;
    animation: bg-pulse 2s infinite ease-out;
}

@keyframes bg-pulse {
    0% {
        transform: scale(1);
        opacity: 0.5;
    }

    100% {
        transform: scale(2.5);
        opacity: 0;
    }
}

.status-indicator {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-muted);
}

.battery-level {
    background: rgba(255, 255, 255, 0.1);
    padding: 0.2rem 0.5rem;
    border-radius: var(--radius-sm);
    font-family: var(--font-mono);
}

.dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background: #6B7280;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
}

.dot.connected {
    background: var(--zone-fat);
    box-shadow: 0 0 10px var(--zone-fat);
}

/* Tabs */
.view-tabs {
    display: flex;
    gap: 0.5rem;
    background: rgba(0, 0, 0, 0.3);
    padding: 0.35rem;
    border-radius: var(--radius-sm);
    align-self: flex-start;
}

.tab {
    background: transparent;
    border: none;
    color: var(--text-muted);
    padding: 0.5rem 1.25rem;
    font-size: 0.9rem;
    font-weight: 600;
    border-radius: calc(var(--radius-sm) - 2px);
    cursor: pointer;
    transition: var(--transition);
}

.tab.active {
    background: rgba(239, 68, 68, 0.15);
    color: var(--primary);
}

.tab:hover:not(.active) {
    background: rgba(255, 255, 255, 0.05);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    font-family: var(--font-sans);
    font-weight: 600;
    border-radius: var(--radius-sm);
    border: 1px solid transparent;
    cursor: pointer;
    transition: var(--transition);
    padding: 0.6rem 1.25rem;
    font-size: 0.95rem;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.btn.primary {
    background: var(--primary);
    color: white;
    box-shadow: 0 4px 15px rgba(239, 68, 68, 0.3);
}

.btn.primary:hover:not(:disabled) {
    background: var(--primary-hover);
    transform: translateY(-1px);
}

.btn.primary.danger {
    background: #DC2626;
}

.btn.ghost {
    background: rgba(255, 255, 255, 0.05);
    color: var(--text-main);
    border-color: var(--glass-border);
}

.btn.ghost:hover {
    background: rgba(255, 255, 255, 0.1);
}

.btn.large {
    padding: 0.8rem 1.5rem;
    font-size: 1.05rem;
}

.btn.small {
    padding: 0.4rem 0.8rem;
    font-size: 0.85rem;
}

.w-full {
    width: 100%;
}

/* Dashboard Grid */
.monitor-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1.5rem;
    margin-top: 1.5rem;
}

.panel-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

.panel-header h2 {
    font-size: 1.1rem;
    font-weight: 600;
}

/* Main BPM Panel */
.main-bpm-panel {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 1.5rem;
}

.bpm-header {
    width: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.bpm-header h2 {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-muted);
}

.zone-badge {
    padding: 0.3rem 0.75rem;
    border-radius: var(--radius-pill);
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    color: #fff;
    transition: background-color 0.5s ease;
}

.bg-rest {
    background: var(--zone-rest);
}

.bg-fat {
    background: var(--zone-fat);
    color: #000;
}

.bg-cardio {
    background: var(--zone-cardio);
    color: #000;
}

.bg-peak {
    background: var(--zone-peak);
    box-shadow: 0 0 15px var(--zone-peak);
}

.bpm-display {
    display: flex;
    align-items: center;
    gap: 1.5rem;
}

.heart-anim {
    filter: drop-shadow(0 0 15px rgba(239, 68, 68, 0.4));
    transition: transform 0.1s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.heart-beat {
    transform: scale(1.15);
}

.bpm-value {
    display: flex;
    align-items: baseline;
    gap: 0.25rem;
}

.bpm-value span:first-child {
    font-family: var(--font-mono);
    font-size: 4rem;
    font-weight: 800;
    line-height: 1;
    color: var(--text-main);
}

.bpm-value .unit {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-muted);
}

.zone-bar {
    width: 100%;
    height: 8px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: var(--radius-pill);
    overflow: hidden;
}

.zone-fill {
    height: 100%;
    border-radius: var(--radius-pill);
    transition: width 0.5s cubic-bezier(0.4, 0, 0.2, 1), background-color 0.5s ease;
}

.zone-labels {
    width: 100%;
    display: flex;
    justify-content: space-between;
    font-size: 0.7rem;
    color: var(--text-muted);
    font-weight: 600;
    text-transform: uppercase;
}

/* Session Panel */
.session-panel {
    display: flex;
    flex-direction: column;
}

.session-controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
}

.timer {
    font-family: var(--font-mono);
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary);
    text-shadow: 0 0 10px rgba(239, 68, 68, 0.3);
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1rem;
    margin-top: auto;
}

.stat-card {
    background: rgba(0, 0, 0, 0.3);
    padding: 1rem;
    border-radius: var(--radius-sm);
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    border: 1px solid rgba(255, 255, 255, 0.05);
    text-align: center;
}

.stat-lbl {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-weight: 600;
    text-transform: uppercase;
}

.stat-val {
    font-family: var(--font-mono);
    font-size: 1.25rem;
    font-weight: 700;
}

/* Chart Panel */
.chart-panel {
    grid-column: 1 / -1;
}

.live-badge {
    background: rgba(239, 68, 68, 0.15);
    color: var(--primary);
    padding: 0.2rem 0.5rem;
    font-size: 0.7rem;
    font-weight: 800;
    border-radius: 4px;
    animation: blink 2s infinite;
}

@keyframes blink {

    0%,
    100% {
        opacity: 1;
    }

    50% {
        opacity: 0.3;
    }
}

.chart-container {
    width: 100%;
    height: 200px;
    position: relative;
}

canvas {
    width: 100%;
    height: 100%;
}

/* History Data Table */
.table-container {
    overflow-x: auto;
}

.data-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}

.data-table th,
.data-table td {
    padding: 1rem;
    text-align: left;
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.data-table th {
    color: var(--text-muted);
    font-weight: 600;
}

.data-table tbody tr:hover {
    background: rgba(255, 255, 255, 0.02);
}

.empty-state {
    text-align: center;
    padding: 4rem 1rem;
    color: rgba(254, 202, 202, 0.5);
    font-style: italic;
}

/* Fallback Msg */
.fullscreen-msg {
    position: fixed;
    inset: 0;
    background: var(--bg-dark);
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
}

.msg-box {
    max-width: 400px;
    padding: 2rem;
}

@media (max-width: 800px) {
    .monitor-grid {
        grid-template-columns: 1fr;
    }
}