:root {
    --bg: #f4f7fb;
    --panel: #ffffff;
    --ink: #182033;
    --muted: #667085;
    --primary: #1167b1;
    --sidebar: #111827;
    --line: #dbe3ef;
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    background: var(--bg);
    color: var(--ink);
    font-family: Arial, Helvetica, sans-serif;
}

.app-shell {
    display: grid;
    grid-template-columns: 260px minmax(0, 1fr);
    min-height: 100vh;
}

.sidebar {
    background: var(--sidebar);
    color: #fff;
    padding: 22px 16px;
}

.brand {
    display: flex;
    align-items: center;
    gap: 10px;
    color: inherit;
    font-weight: 700;
    text-decoration: none;
}

.brand-mark {
    display: inline-grid;
    place-items: center;
    width: 38px;
    height: 38px;
    border-radius: 8px;
    background: var(--primary);
    color: #fff;
}

.sidebar nav {
    display: grid;
    gap: 4px;
    margin-top: 28px;
}

.sidebar nav a {
    color: #d7deea;
    padding: 10px 12px;
    border-radius: 7px;
    text-decoration: none;
}

.sidebar nav a:hover {
    background: rgba(255,255,255,.08);
    color: #fff;
}

.app-main {
    padding: 24px;
    min-width: 0;
}

.topbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 22px;
}

.topbar h1,
.login-card h1 {
    margin: 0;
    font-size: 1.75rem;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 16px;
    margin-bottom: 20px;
}

.stat-card,
.content-panel,
.login-card {
    background: var(--panel);
    border: 1px solid var(--line);
    border-radius: 8px;
    box-shadow: 0 10px 30px rgba(16, 24, 40, .06);
}

.stat-card {
    padding: 18px;
}

.stat-card span {
    display: block;
    color: var(--muted);
}

.stat-card strong {
    display: block;
    font-size: 2rem;
}

.content-panel {
    padding: 20px;
}

.content-panel h2 {
    margin: 0;
    font-size: 1.2rem;
}

.login-page {
    display: grid;
    place-items: center;
    min-height: 100vh;
    padding: 20px;
}

.login-card {
    width: min(100%, 420px);
    padding: 28px;
}

@media (max-width: 900px) {
    .app-shell {
        grid-template-columns: 1fr;
    }

    .sidebar {
        position: static;
    }

    .stats-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }
}

@media (max-width: 560px) {
    .app-main {
        padding: 16px;
    }

    .topbar {
        align-items: flex-start;
        gap: 12px;
        flex-direction: column;
    }

    .stats-grid {
        grid-template-columns: 1fr;
    }
}