SVB purchased corporate bonds that declined in value, but didn't decline all the way to zero. They still have those bonds, and I believe they can still be sold for > 80% of the price they paid.
The issue is that the bonds can’t be sold now for anything like npv, because nearly risk-feee government issued bonds pay 3-4x what these bonds will.
That makes them… discounted
The actual value of the bond went down, because the expected value of the payout is less, even though the actual amount of dollars returned at maturity is the same.
Which is why the market price for it went down.