react/packages/react-devtools-shared/src/devtools/ContextMenu/ContextMenu.css

.ContextMenu {
  position: absolute;
  background-color: var(--color-context-background);
  box-shadow: 1px 1px 2px var(--color-shadow);
  border-radius: 0.25rem;
  overflow: hidden;
  z-index: 10000002;
  user-select: none;
}