Although we have made a point of the fact that we code HTML, CSS, PHP and JavaScript at Fast Fix Web Design, the majority of our clients are WordPress websites. However, we also do sub-contract website maintenance for both HTML and WordPress sites. This is one of the sites that we maintain using straight up html and css.
In general, IMHO, every WordPress “developer” should be competent with html and css because WordPress is simply an engine that generates HTML and CSS to create websites. If you can’t write the code, how can you really work with the code?