Key TakeawaysCostco's net sales during the five-week December period improved 10% year-over-year.Holiday period sales beat analysts' expectations amid improving consumer spending environment, JPMorgan said.Citi analysts said they expect the stock to see "modest strength" after shares pulled back from a record high last month. Costco Wholesale (COST) posted holiday sales figures Wednesday that blew past analysts' expectations.  The membership-based retailer reported net sales of $27.52 billion in the five-we ...