TLDR - Credit Suisse has been a sh*t show for over a decade. This has been coming for a while.

Credit Suisse is in investment banking and wealth management. It does not have a significant retail presence (EDIT - outside of Switzerland). Credit Suisse has also had a number of accounting, risk management, and other scandals over the last few years. They were bailed out late last year by a fund linked with Saudi Arabia who took a ~10% stake in the company. Today, they (the Saudi fund) refused to inject more capital and the shares have collapsed.