I do not know which browser supports this, but you can pass a formula to :nth-of-type():
ul li:nth-of-type(1n+4) {display: none;} /* should match your case */
Further details on: http://www.w3schools.com/cssref/sel_nth-of-type.asp
Edit
I altered it from (n+4) to (1n+4) since the first version works but isn't valid. I use this in media queries to hide cut-down items on smaller screens.
Example:
b:nth-of-type(1n+4){ opacity:.3; }
<b>1</b>
<b>2</b>
<b>3</b>
<b>4</b>
<b>5</b>
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