#1: Web Designers don’t need HTML/CSS knowledge
They do. Period. Not an advanced one, but at least the basics… What is the difference between a designer and a web designer that doesn’t know the basics of a web page? None.
Far too many times, I had to implement a design that is outright impossible to make, or hard to change, or is totally inefficient performance-wise. Imagine if an an architect presented a concept with a floating building… Fortunately for most engineers, most people are familiar with basic laws of physics, so the aforementioned architect will be put in a straitjacket right away.
#2: Learn the basics
You want to be a web designer, not just designer… I’m sorry, but you’ll need to specialize a bit more. I can throw a few concepts in Photoshop, Illustrator, or XD, but that does not make me a designer. Basic knowledge of HTML/CSS will help you to understand the limitations. If your team uses some CSS framework, check it out. Try to use most of its templates, don’t make the developers override an entire thing.
#3: Think, dammit
Some designs I saw so far… You don’t even need to know anything about web or design to figure out that they’re wrong. Pop-up dialogues within pop-up dialogues, disregard for different screen sizes / logical responsive behavior… I could continue with even more bizarre examples, but these two are the most frequent… and something I simply can’t understand…