:root {
    --color-bg: #f8fafc;
    --color-surface: #ffffff;
    --color-surface-hover: #f1f5f9;
    --color-border: #e2e8f0;
    --color-text: #0f172a;
    --color-muted: #64748b;
    --color-primary: #2563eb;
    --color-primary-dark: #1d4ed8;
    --color-primary-light: #eff6ff;
    --color-success: #10b981;
    --color-success-bg: #ecfdf5;
    --color-danger: #ef4444;
    --color-danger-bg: #fef2f2;
    --color-warning: #f59e0b;
    --color-warning-bg: #fffbeb;
    --color-info: #06b6d4;
    --color-info-bg: #ecfeff;
    --radius: 12px;
    --radius-sm: 8px;
    --shadow-sm: 0 1px 2px 0 rgba(15, 23, 42, 0.05);
    --shadow: 0 4px 6px -1px rgba(15, 23, 42, 0.05), 0 2px 4px -2px rgba(15, 23, 42, 0.05);
    --shadow-lg: 0 10px 15px -3px rgba(15, 23, 42, 0.08), 0 4px 6px -4px rgba(15, 23, 42, 0.04);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    font-size: 14px;
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
}

a {
    color: var(--color-primary);
    text-decoration: none;
    transition: color 0.15s ease;
}
a:hover {
    color: var(--color-primary-dark);
}

/* App Header */
.app-header {
    background: rgba(255, 255, 255, 0.92);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--color-border);
    position: sticky;
    top: 0;
    z-index: 100;
}

.app-header__inner {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.75rem 1.25rem;
    gap: 1.5rem;
}

.brand {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 700;
    font-size: 1.15rem;
    color: var(--color-text);
}
.brand-icon {
    color: var(--color-primary);
    flex-shrink: 0;
}
.brand:hover {
    color: var(--color-primary);
    text-decoration: none;
}

/* Mobile Nav Toggle Button */
.nav-toggle {
    display: none;
    flex-direction: column;
    justify-content: space-between;
    width: 32px;
    height: 24px;
    background: transparent;
    border: none;
    cursor: pointer;
    padding: 0;
    z-index: 101;
}

.nav-toggle__bar {
    width: 100%;
    height: 3px;
    background-color: var(--color-text);
    border-radius: 3px;
    transition: transform 0.25s ease, opacity 0.25s ease;
}

.nav-toggle.is-open .nav-toggle__bar:nth-child(1) {
    transform: translateY(10.5px) rotate(45deg);
}
.nav-toggle.is-open .nav-toggle__bar:nth-child(2) {
    opacity: 0;
}
.nav-toggle.is-open .nav-toggle__bar:nth-child(3) {
    transform: translateY(-10.5px) rotate(-45deg);
}

/* Nav Collapse Menu */
.nav-collapse {
    display: flex;
    align-items: center;
    justify-content: space-between;
    flex: 1;
}

.main-nav {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}
.main-nav a {
    color: var(--color-muted);
    font-weight: 600;
    padding: 0.45rem 0.85rem;
    border-radius: var(--radius-sm);
    transition: all 0.15s ease;
}
.main-nav a:hover {
    color: var(--color-text);
    background: var(--color-surface-hover);
    text-decoration: none;
}
.main-nav a.active {
    color: var(--color-primary);
    background: var(--color-primary-light);
}

.user-menu {
    display: flex;
    align-items: center;
    gap: 0.85rem;
}
.user-badge {
    background: var(--color-surface-hover);
    padding: 0.35rem 0.75rem;
    border-radius: 999px;
    font-weight: 600;
    font-size: 0.82rem;
    color: var(--color-text);
}

.link-button {
    background: none;
    border: none;
    color: var(--color-muted);
    cursor: pointer;
    font: inherit;
    font-weight: 600;
    padding: 0.35rem 0.75rem;
    border-radius: var(--radius-sm);
    transition: all 0.15s ease;
}
.link-button:hover {
    color: var(--color-danger);
    background: var(--color-danger-bg);
}
.inline-form { display: inline; }

/* Main Content Container */
.app-main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1.5rem 1.25rem 3rem;
}

/* Page Header */
.page-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
    gap: 1rem;
}
.page-header h1 {
    margin: 0;
    font-size: 1.5rem;
    font-weight: 700;
    letter-spacing: -0.02em;
}
.page-header__actions {
    display: flex;
    gap: 0.65rem;
    flex-wrap: wrap;
}

/* Messages / Alerts */
.messages {
    list-style: none;
    padding: 0;
    margin: 0 0 1.25rem;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}
.message {
    padding: 0.85rem 1.15rem;
    border-radius: var(--radius-sm);
    font-weight: 500;
    box-shadow: var(--shadow-sm);
}
.message--success { background: var(--color-success-bg); color: #065f46; border: 1px solid #a7f3d0; }
.message--error { background: var(--color-danger-bg); color: #991b1b; border: 1px solid #fecaca; }
.message--warning { background: var(--color-warning-bg); color: #92400e; border: 1px solid #fde68a; }
.message--info, .message--debug { background: var(--color-info-bg); color: #155e75; border: 1px solid #a5f3fc; }

.alert {
    padding: 0.85rem 1.15rem;
    border-radius: var(--radius-sm);
    font-weight: 500;
    margin-bottom: 1rem;
}
.alert--error { background: var(--color-danger-bg); color: #991b1b; border: 1px solid #fecaca; }

/* Stat Cards Grid */
.stat-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 1rem;
    margin-bottom: 1.75rem;
}
.stat-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 1.15rem 1.25rem;
    box-shadow: var(--shadow-sm);
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
    transition: transform 0.15s ease, box-shadow 0.15s ease;
}
.stat-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}
.stat-card__label {
    color: var(--color-muted);
    font-size: 0.78rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
}
.stat-card__value {
    font-size: 1.75rem;
    font-weight: 800;
    letter-spacing: -0.02em;
}
.stat-card--success .stat-card__value { color: var(--color-success); }
.stat-card--muted .stat-card__value { color: var(--color-muted); }
.stat-card--info .stat-card__value { color: var(--color-info); }
.stat-card--warning .stat-card__value { color: var(--color-warning); }

/* Layout Columns & Panels */
.two-col {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1.5rem;
    margin-bottom: 1.5rem;
}

.panel {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 1.35rem 1.5rem;
    box-shadow: var(--shadow-sm);
    margin-bottom: 1.5rem;
}
.panel h2 {
    margin-top: 0;
    font-size: 1.15rem;
    font-weight: 700;
    letter-spacing: -0.01em;
}
.panel--narrow {
    max-width: 560px;
    margin: 0 auto 1.5rem;
}

/* Filter Bar */
.filter-bar {
    display: flex;
    gap: 0.65rem;
    margin-bottom: 1.25rem;
    flex-wrap: wrap;
    align-items: center;
}
.filter-bar .form-control, .filter-bar .form-select {
    flex: 1;
    min-width: 140px;
}

/* Form Controls & Inputs */
.form-control, .form-select, input[type="text"], input[type="password"], input[type="email"], input[type="number"], select, textarea {
    width: 100%;
    padding: 0.65rem 0.85rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    font-size: 0.9rem;
    background: var(--color-surface);
    color: var(--color-text);
    outline: none;
    transition: border-color 0.15s ease, box-shadow 0.15s ease;
    min-height: 42px;
}
.form-control:focus, .form-select:focus, input:focus, select:focus, textarea:focus {
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}
.form-control:disabled, input:disabled {
    background: #f1f5f9;
    color: var(--color-muted);
}
.form-group {
    margin-bottom: 1.15rem;
}
.form-group label {
    display: block;
    margin-bottom: 0.4rem;
    font-weight: 600;
    font-size: 0.85rem;
}
.field-help {
    color: var(--color-muted);
    font-size: 0.8rem;
    margin: 0.35rem 0 0;
}
.field-error {
    color: var(--color-danger);
    font-size: 0.8rem;
    margin: 0.35rem 0 0;
    font-weight: 500;
}
.form-actions {
    display: flex;
    gap: 0.75rem;
    margin-top: 1.5rem;
    flex-wrap: wrap;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.6rem 1.15rem;
    border-radius: var(--radius-sm);
    border: 1px solid transparent;
    font-weight: 600;
    font-size: 0.875rem;
    cursor: pointer;
    text-align: center;
    transition: all 0.15s ease;
    min-height: 42px;
    gap: 0.4rem;
}
.btn:hover {
    text-decoration: none;
    transform: translateY(-1px);
}
.btn:active {
    transform: translateY(0);
}
.btn--primary {
    background: var(--color-primary);
    color: #ffffff;
    box-shadow: 0 2px 4px rgba(37, 99, 235, 0.2);
}
.btn--primary:hover {
    background: var(--color-primary-dark);
    color: #ffffff;
}
.btn--secondary {
    background: #e2e8f0;
    color: var(--color-text);
}
.btn--secondary:hover {
    background: #cbd5e1;
}
.btn--ghost {
    background: transparent;
    border-color: var(--color-border);
    color: var(--color-text);
}
.btn--ghost:hover {
    background: var(--color-surface-hover);
    border-color: #cbd5e1;
}
.btn--danger {
    background: var(--color-danger);
    color: #ffffff;
}
.btn--danger:hover {
    background: #dc2626;
}
.btn--danger-ghost {
    background: transparent;
    border-color: #fca5a5;
    color: var(--color-danger);
}
.btn--danger-ghost:hover {
    background: var(--color-danger-bg);
}
.btn--sm {
    padding: 0.35rem 0.75rem;
    font-size: 0.8rem;
    min-height: 34px;
}
.btn--block {
    width: 100%;
    display: flex;
}

/* Data Tables */
.table-responsive {
    width: 100%;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    border-radius: var(--radius-sm);
}

.data-table {
    width: 100%;
    border-collapse: collapse;
}
.data-table th, .data-table td {
    text-align: left;
    padding: 0.75rem 0.85rem;
    border-bottom: 1px solid var(--color-border);
}
.data-table th {
    font-size: 0.75rem;
    text-transform: uppercase;
    color: var(--color-muted);
    letter-spacing: 0.05em;
    font-weight: 700;
    background: #f8fafc;
}
.data-table tbody tr:hover {
    background-color: var(--color-surface-hover);
}
.actions-col {
    white-space: nowrap;
    display: flex;
    gap: 0.4rem;
    align-items: center;
}

/* Badges */
.badge {
    display: inline-block;
    padding: 0.25rem 0.65rem;
    border-radius: 999px;
    font-size: 0.75rem;
    font-weight: 700;
    letter-spacing: 0.02em;
}
.badge--active, .badge--ACTIVE { background: var(--color-success-bg); color: #065f46; border: 1px solid #a7f3d0; }
.badge--inactive, .badge--INACTIVE { background: #f1f5f9; color: #475569; border: 1px solid #e2e8f0; }
.badge--maintenance, .badge--MAINTENANCE { background: var(--color-warning-bg); color: #92400e; border: 1px solid #fde68a; }
.badge--muted { background: #f1f5f9; color: #64748b; }

/* Trends */
.trend { font-weight: 700; }
.trend--up { color: var(--color-success); }
.trend--down { color: var(--color-danger); }
.trend--flat { color: var(--color-muted); }

/* Detail List */
.detail-list {
    display: grid;
    grid-template-columns: 160px 1fr;
    row-gap: 0.75rem;
    margin: 0;
}
.detail-list dt {
    color: var(--color-muted);
    font-weight: 600;
}
.detail-list dd {
    margin: 0;
    font-weight: 500;
}

.big-reading {
    font-size: 2.2rem;
    font-weight: 800;
    margin: 0.25rem 0 1rem;
    letter-spacing: -0.03em;
}
.big-reading .unit {
    font-size: 1rem;
    font-weight: 500;
    color: var(--color-muted);
}

.simple-list {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-direction: column;
    gap: 0.65rem;
}
.simple-list li {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-bottom: 0.65rem;
    border-bottom: 1px solid var(--color-border);
}

.pagination {
    display: flex;
    gap: 0.75rem;
    align-items: center;
    justify-content: center;
    margin-top: 1.25rem;
    font-size: 0.85rem;
}
.pagination a { font-weight: 600; }
.pagination__current { color: var(--color-muted); }

.muted { color: var(--color-muted); }
.small { font-size: 0.8rem; }

/* Auth Pages */
.auth-page {
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 75vh;
    padding: 1.5rem 1rem;
}
.auth-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 2.25rem 2rem;
    width: 100%;
    max-width: 400px;
    box-shadow: var(--shadow-lg);
}
.auth-card h1 {
    margin-top: 0;
    font-size: 1.5rem;
    font-weight: 800;
    letter-spacing: -0.02em;
}

.track-panel { max-width: 480px; }
.track-info__row {
    display: flex;
    gap: 1rem;
    margin-bottom: 1.25rem;
}
.track-info__row > div { flex: 1; }
.track-info__label {
    display: block;
    font-size: 0.78rem;
    font-weight: 700;
    color: var(--color-muted);
    text-transform: uppercase;
    margin-bottom: 0.3rem;
}
.track-info__last {
    background: #f8fafc;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    padding: 0.85rem 1rem;
    margin-bottom: 1.25rem;
}
.last-reading-value {
    font-size: 1.4rem;
    font-weight: 800;
    margin: 0.15rem 0;
}
.track-form {
    border-top: 1px solid var(--color-border);
    padding-top: 1.25rem;
}

/* ==========================================================================
   Mobile Responsive Breakpoints
   ========================================================================== */

@media (max-width: 768px) {
    .nav-toggle {
        display: flex;
    }

    .nav-collapse {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--color-surface);
        border-bottom: 1px solid var(--color-border);
        box-shadow: var(--shadow-lg);
        flex-direction: column;
        padding: 1rem 1.25rem;
        gap: 1rem;
        align-items: stretch;
    }

    .nav-collapse.is-open {
        display: flex;
    }

    .main-nav {
        flex-direction: column;
        align-items: stretch;
        gap: 0.35rem;
    }

    .main-nav a {
        padding: 0.65rem 0.85rem;
    }

    .user-menu {
        flex-direction: column;
        align-items: stretch;
        padding-top: 0.85rem;
        border-top: 1px solid var(--color-border);
        gap: 0.65rem;
    }

    .user-badge {
        text-align: center;
    }

    .logout-btn {
        width: 100%;
        text-align: center;
        justify-content: center;
    }

    .two-col {
        grid-template-columns: 1fr;
    }

    .page-header {
        flex-direction: column;
        align-items: stretch;
    }

    .page-header__actions {
        width: 100%;
    }

    .page-header__actions .btn {
        flex: 1;
    }

    .detail-list {
        grid-template-columns: 1fr;
        gap: 0.25rem;
    }

    .detail-list dt {
        font-size: 0.78rem;
        text-transform: uppercase;
        margin-top: 0.5rem;
    }
}

@media (max-width: 580px) {
    .app-main {
        padding: 1.25rem 0.85rem 2.5rem;
    }

    .stat-grid {
        grid-template-columns: 1fr 1fr;
        gap: 0.75rem;
    }

    .stat-card {
        padding: 0.85rem 1rem;
    }

    .stat-card__value {
        font-size: 1.4rem;
    }

    .filter-bar {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 0.5rem;
    }

    .filter-bar input[name="q"] {
        grid-column: 1 / -1;
    }

    .filter-bar input[name="customer"] {
        grid-column: 1 / -1;
    }

    .filter-bar .btn {
        min-height: 38px;
    }

    .panel {
        padding: 1rem;
    }

    .data-table {
        display: block;
        width: 100%;
        overflow-x: auto;
        white-space: nowrap;
    }

    .track-info__row {
        flex-direction: column;
        gap: 0.5rem;
    }

    .form-actions {
        flex-direction: column;
    }

    .form-actions .btn {
        width: 100%;
    }
}