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

:root {
    --sidebar-width: 240px;
    --sidebar-collapsed-width: 64px;
    --sidebar-bg: #1e293b;
    --sidebar-text: #cbd5e1;
    --sidebar-active: #3b82f6;
    --sidebar-hover: #334155;
    --main-bg: #f8fafc;
    --text-color: #1e293b;
    --border-color: #e2e8f0;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    color: var(--text-color);
    background: var(--main-bg);
    line-height: 1.6;
}

.layout {
    display: flex;
    min-height: 100vh;
}

.main-content {
    flex: 1;
    margin-left: var(--sidebar-width);
    padding: 2rem;
    transition: margin-left 0.3s ease;
}

.layout.sidebar-collapsed .main-content {
    margin-left: var(--sidebar-collapsed-width);
}

@media (max-width: 768px) {
    .main-content {
        margin-left: 0;
        padding: 1rem;
    }
}

h1, h2, h3 { margin-bottom: 0.5rem; }
a { color: var(--sidebar-active); text-decoration: none; }
a:hover { text-decoration: underline; }

.btn {
    display: inline-block;
    padding: 0.5rem 1rem;
    border: none;
    border-radius: 0.375rem;
    font-size: 0.875rem;
    cursor: pointer;
    transition: background 0.2s;
}

.btn-primary {
    background: var(--sidebar-active);
    color: #fff;
}

.btn-primary:hover {
    background: #2563eb;
}