> HTML / CSS: You should know all of this, but back-end developers generally don't have to do most of the heavy lifting here. It's very easy to hire someone to

> HTML / CSS: You should know all of this, but back-end developers generally don't have to do most of the heavy lifting here. It's very easy to hire someone to turn your PSD's into HTML / CSS and then the back-end devs can take it from there. In an ideal world, yes. Unfortunately, you can often end up with HTML templates and CSS stylesheets that might fit the bill visually but simply aren't fit for purpose in other ways. As developers we need to consider factors such as the behaviour of the page and maintainability of the system as a whole. A badly designed stylesheet may be brittle and resistant to change or may even do things in a way that is incompatible with the frameworks and tools that you are using, and many designers aren't even aware that such constraints exist, let alone what problems they may cause. For example, I was once given a CSS stylesheet to work with (for which the client had paid quite a large sum of money) that declared <span> as a block-level element. This caused no end of chaos when we had to use it along with ASP.NET validator controls on a WebForms page, which of course makes liberal use of <span> tags for inline validation messages.