.cite-navigation {
  position: fixed;
  top: 0;
  left: 0;
  width: 240px;
  height: 100vh;
  overflow-y: auto;
  background: #f4f4f4;
  padding: 1em;
  border-right: 1px solid #ccc;
  box-sizing: border-box;
  z-index: 1000;
}

body {
  margin-left: 260px; /* ← ここが最重要 */
}