* { box-sizing: border-box; }

html, body {
  height: 100%;
  margin: 0;
  padding: 0;
  overflow: hidden;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  background: #f6f7fb;
  color: #111827;
}

:root {
  --bg: #f6f7fb;
  --panel: #ffffff;
  --panel-2: #f0f2f7;
  --fg: #111827;
  --muted: #6b7280;
  --border: #e5e7eb;
  --brand: #2563eb;
  --brand-2: #1d4ed8;
  --radius: 12px;
  --sidebar-w: 260px;
  --header-h: 60px;
}

/* HEADER */
.app-header {
  background-color: #FBB000 !important;
  height: var(--header-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 16px;
  border-bottom: 1px solid var(--border);
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  font-weight: 700;
  font-size: 16px;
}

.brand-logo {
  height: 36px;
  width: auto;
}

/* LAYOUT */
.app-shell {
  display: grid;
  grid-template-columns: var(--sidebar-w) 1fr;
  height: calc(100vh - var(--header-h));
  overflow: hidden;
}

/* SIDEBAR */
.app-sidebar {
  margin-top: 20px;
  background: var(--panel);
  border-right: 1px solid var(--border);
  padding: 14px;
  overflow-y: auto;
}

.nav-item {
  display: block;
  padding: 10px 12px;
  border-radius: 8px;
  color: var(--fg);
  text-decoration: none;
}

.nav-item:hover {
  background: var(--panel-2);
}

/* MAIN CONTENT */
.app-main {
  padding: 16px;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
}

/* CONTENT BOX */
.content-body {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
  flex: 1;
  display: flex;
  flex-direction: column;
}

/* IFRAME */
#book_link {
  width: 100%;
  flex: 1;           
  min-height: 600px;
  border: none;
}

/* FOOTER */
.app-footer {
  margin-top: 12px;
  color: var(--muted);
  font-size: 13px;
}

/* MOBILE */
@media (max-width: 860px) {
  .app-shell {
    grid-template-columns: 1fr;
  }

  .app-sidebar {
    border-right: none;
    border-bottom: 1px solid var(--border);
  }
}