We have a long-standing checklist for merge requests. However, it hardly matches the intricate requirements for design. This checklist fills the gap.

Before starting implementing, look at all designs: are there components similar to yours? Have they already been implemented? Can you build on this prior art when implementing yours?

Checklist: I confirm my design implementation

• has been tested manually by me
• adheres to the code style of the project (e.g. BEM)
• avoids "magic numbers" (don't say e.g. padding: 20px)
• does not duplicate existing styles (for similar parts)
• respects all specifications of the design
  • spacings and sizes are correct
  • on small viewports, elements are sometimes sized differently compared to large viewports
  • edge cases have been catered for
• is responsive. When scaling a browser window from 320px to 3000px width (try negative browser zoom):
  • it looks good all the way
  • all functionality remains usable (e.g. when implementing a navigation)
• works on touch devices. About 50% of website visitors use a smartphone nowadays (depending on the website). Especially hover styles loose relevance in this light. A touch user:
  • can perform all interactions
  • can see all information
• works in all expected contexts (e.g. solitary, in a sidebar, on a dark background etc.)
• is accessible. See Barrierefreie Webseiten.
  • It navigates through elements in order (or in an order that makes sense). You can test that by clicking into the page, top/left of the new design, and repeatedly pressing the tab key.
  • It highlights interactive elements on focus (e.g. through :focus-visible).
  • Interactive elements without a text label have an aria-label.
• uses Semantic HTML
• is well usable. Interacting with the component:
  • feels natural
  • does not require unnecessary steps (e.g. when pressing a "search" icon, shows the search field already focused)
  • adheres to common conventions (e.g. backdrop click closes an overlay)
• is correctly localized (if applicable)
  • all texts
  • date/number/currency/… formats

Bonus

Add screenshots of any new or changed elements. Gitlab has a "Details block" behind the "+" button in its WYSIWYG editor that helps saving space.