File this under things you usually find out about the hard way: Stylesheet Limits in Internet Explorer. For IE 6 – 9 the limits are:
– A sheet may contain up to 4095 rules
– A sheet may @import up to 31 sheets
– @import nesting supports up to 4 levels deep
In IE 10 these were increased to:
– A sheet may contain up to 65534 rules
– A document may use up to 4095 stylesheets
– @import nesting is limited to 4095 levels (due to the 4095 stylesheet limit)
I haven’t been able to find data on similar limits for Chrome, Firefox, or Safari.