SUCCESS Rules from the stylesheet: #a:nth-child(n-1) { color: green; } #b:nth-child(n- 10) { color: green; } #g:nth-child(-n-1) { color: green; } #h:nth-child(-n- 10) { color: green; } #n:nth-child(-n - 1) { color: green; } #o:nth-child(-n +13) { color: green; } Expected result: #a:nth-child(n-1) { color: green; } #b:nth-child(n- 10) { color: green; } #g:nth-child(-n-1) { color: green; } #h:nth-child(-n- 10) { color: green; } #n:nth-child(-n - 1) { color: green; } #o:nth-child(-n +13) { color: green; }