:root {
    --bg-color: #0d1117;
    --card-bg: rgba(22, 27, 34, 0.8);
    --accent-color: #58a6ff;
    --text-main: #c9d1d9;
    --text-muted: #8b949e;
    --border-color: #30363d;
    --success-color: #238636;
}

body {
    margin: 0;
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    display: flex;
    flex-direction: column;
    height: 100vh;
    overflow: hidden;
}

/* --- Navigation Bar --- */
nav {
    display: flex;
    justify-content: center;
    background: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
    padding: 10px 0;
    backdrop-filter: blur(10px);
    z-index: 100;
}

.nav-item {
    padding: 10px 20px;
    margin: 0 5px;
    cursor: pointer;
    border-radius: 6px;
    transition: all 0.2s ease;
    font-weight: 600;
    color: var(--text-muted);
}

.nav-item.active {
    background: rgba(88, 166, 255, 0.15);
    color: var(--accent-color);
}

.nav-item:hover:not(.active) {
    background: rgba(255, 255, 255, 0.05);
}

/* --- Content Views --- */
.view-container {
    flex: 1;
    position: relative;
}

.view {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    display: none;
    flex-direction: column;
    padding: 20px;
    overflow-y: auto;
}

.view.active {
    display: flex;
}

/* --- Management UI --- */
.management-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 20px;
    max-width: 1000px;
    margin: 0 auto;
    width: 100%;
    padding-bottom: 520px;
}

.card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 24px;
    transition: transform 0.2s ease;
}

.card h2 {
    margin-top: 0;
    font-size: 1.2rem;
    color: var(--accent-color);
}

.card p {
    color: var(--text-muted);
    font-size: 0.9rem;
    margin-bottom: 20px;
}

.upload-btn {
    display: block;
    width: 100%;
    padding: 12px;
    background: var(--accent-color);
    color: white;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    font-weight: 600;
    text-align: center;
}

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

input[type="file"] {
    display: none;
}

.file-label {
    display: block;
    border: 2px dashed var(--border-color);
    padding: 20px;
    text-align: center;
    border-radius: 8px;
    margin-bottom: 15px;
    cursor: pointer;
}

.file-label:hover {
    border-color: var(--accent-color);
}

/* --- Fitbit Card --- */
.fitbit-card {
    grid-column: 1 / -1;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.fitbit-card .btn-secondary {
    background: var(--success-color);
}

/* --- Fullscreen Dashboard --- */
#dashboard-iframe {
    width: 100%;
    height: 100%;
    border: none;
}