I'm working on a UX/UI process for my project, however I'm confused to understand the approach between UX/UI and front-end.
After a .psd is developed, who would be responsible to transform it into html/css?
It entirely depend on your organizational structure as to who would be responsible to transform the psd designs to html/css.
But in a typical scenario, a designer is expected to take up their PSD files and prepare a set of image assets to be used in HTML/CSS and also create a specification document defining all styles used alongwith sizes. This specifications document should also capture any transitions/effects desired in the designed files.
Thereafter this document is typically passed onto either a front-end developer or to the core developer team who is responsible for writing html/css for the same.
In some cases however, it is the designer's responsibility to deliver the css file with all styles defined and then the dev team will build html around the defined css.
In my company this is how it goes:
Interaction Designers are tasked with conceptualizing, and implementing high fidelity wireframes to give to the visual designer. Wireframes are annotated (this means we specify what certain elements do what, like if a modal pops up, we want it to bounce three times for instance).
Once we have all the wireframes annotated and sent to the visual designer for visual treatment, we then send it to the front-end back-end developers to implement what is needed to be done. They then follow the visual design and get the assets from the designer, while also paying attention to the annotations for exactly what certain things do.
This is a little more complex than what I said, because there is also site maps, user flows, user testing, user research, and so on and so forth, but for your question I think this works.