Apply border only for first set of list evenafter mouseover

[golgi]

\[code\]<ul id="menu"> <li>first set<li> <ul> <li>second set</li> <li>second set</li> </ul> <li>first set<li> <li>first set<li></ul>\[/code\]I have applied border-left for first set of list using\[code\]#menu li{ border-left: 1px solid black;}\[/code\]However when mouseover first set, second set list showing border-left of 2px.But i dont want any border-left for second set. How do i remove this 2px?.I could remove 1px by using\[code\]#menu ul li{ border-left: 0px;}\[/code\]How i can remove another 1px border of second set ?.