* { box-sizing: border-box; margin:0; padding:0; }
body, html { height:100%; font-family: sans-serif; }
header {
  background: #f4f4f4; padding: 8px;
  display: flex; align-items: center; gap: 8px;
  border-bottom: 1px solid #ccc;
}
#container { display: flex; height: calc(100% - 42px); }
#sidebar {
  width: 260px; overflow-y: auto;
  border-right: 1px solid #ccc; padding: 10px;
}
#content {
  flex:1; overflow-y: auto; padding: 20px;
}
#sidebar ul { list-style: none; }
#sidebar li {
  padding: 4px 6px; cursor: pointer;
}
#sidebar li:hover { background: #e0e0e0; }