HTML & CSS is a commodity skill, and most of its mundane parts are going to be automated away soon. Either through a design-to-code workflow like what I'm working on now (https://protoship.io), or with integrated tools like Webflow & Modulz.
There are folks who're able to design in code (Basecamp style), folks who're only able to design in a drawing tool and does not know CSS at all (the Dribbble crowd), and the unicorns that I'm so jealous of who're able to play in both courts masterfully.
But knowing design doesn't have much to do with tools - HTML/CSS or Sketch. I've observed folks from all three categories, and my singular take-away was practice, practice, practice. Some people have an aesthetic bend that gives them an advantage, but most of us can build a basic understanding by being deeply interested in the craft and putting in the hours. Search for "how to be a designer", there is a rich array of resources. Pick a book like The Non-Designer's Design Book, an online course like refactoringui, and a DailyUI challenge. Start deliberate practice. Give it a few hundred hours.
There are folks who're able to design in code (Basecamp style), folks who're only able to design in a drawing tool and does not know CSS at all (the Dribbble crowd), and the unicorns that I'm so jealous of who're able to play in both courts masterfully.
But knowing design doesn't have much to do with tools - HTML/CSS or Sketch. I've observed folks from all three categories, and my singular take-away was practice, practice, practice. Some people have an aesthetic bend that gives them an advantage, but most of us can build a basic understanding by being deeply interested in the craft and putting in the hours. Search for "how to be a designer", there is a rich array of resources. Pick a book like The Non-Designer's Design Book, an online course like refactoringui, and a DailyUI challenge. Start deliberate practice. Give it a few hundred hours.