Depends on the context. When I was a SV biglaw associate, I wore slacks and button down, generally without coat (only for meetings). On 'casual Friday' I wore polo, typically with jeans. Basically, SV law firms are always 'business casual' unless you're going to court or a deposition. And on casual Fridays, it's even less formal.

I assume tech companies are more casual than big law firms, and that things may have gotten more casual in the decade since I left the law.