Designing for Developers: How GitHub's Former Head of Design Built Systems That Scale

Diana Mounter, former Head of Design at GitHub, shares her journey from a UK print shop to leading design for a platform used by over 150 million developers. Discover how embracing technical tools and focusing on user outcomes shaped her approach to building products like GitHub's Dark Mode and Primer design system.

From Print to Digital: An Unconventional Path to Tech

Diana Mounter's design career began unexpectedly through an apprenticeship at a design and print shop in the UK. "I didn't really know web design and graphic design could be a career," she recalls. The work appealed to her as it combined both technical and creative elements—a perfect marriage of her interests.

When the print industry began declining in the UK during the recession, Mounter made a bold decision to move to Australia. "Part of my reason for choosing Australia was like, maybe I'll find a job there. Maybe it'll just be a great experience to see another country and to kind of test myself a bit." She bought a one-way ticket and eventually found work in Australia, where she spent 7-8 years developing her skills.

The GitHub Discovery: Finding Where Design and Code Intersect

Mounter's introduction to GitHub came during a hackathon competition where engineers encouraged her to try the platform. "Something about using GitHub and being in the same place as engineers just sort of sparked this excitement and interest in me," she explains. She began putting her websites on GitHub and learning tools like Jekyll, GitHub's static site generator.

This experience revealed a crucial insight: "There's something exciting about being able to make the thing that you have in your head and build it and put it out there on the internet and other people can use it. There's something that feels really great about that as compared to just being able to make a picture of something."

Joining GitHub: When Passion Meets Opportunity

Mounter's journey to GitHub began with an email from Mark Otto, creator of Bootstrap. "Mark Otto was a bit of a celebrity to me because he had created Bootstrap and if you were interested in design systems, you kind of knew about Bootstrap." Her initial attraction wasn't just to the product but also to GitHub's brand identity, particularly the Octocat mascot.

"I used to like spend late nights just illustrating different variations of the Octocat just for fun because I just loved the brand so much," she admits. The Octocat's origin story itself represents the power of meeting the moment—it was originally a stock illustration placed on a 404 page that developers loved, leading to its adoption as the company's mascot.

Building Primer: Creating GitHub's Design System

During her nearly nine years at GitHub, Mounter helped transform Primer from a CSS framework into a comprehensive ecosystem of components and tooling. She explains that design systems "essentially codify patterns that can be used to design UI" and act as "a language that is shared by designers and developers."

She started improving Primer through grassroots efforts: "I just started poking around starting to suggest some improvements to the CSS and I found that there was quite a few other people at GitHub that also wanted to work on primer and improve the front-end code." The team focused on high-impact changes that addressed major pain points, recognizing that "people will not always react to that in the most positive way" when introducing design system rules.

The Dark Mode Launch: A Lesson in Strategic Design

One of Mounter's most memorable projects was shipping Dark Mode in 2020. The project was particularly challenging because the team had to keep it secret until GitHub's annual conference, preventing them from getting direct customer feedback beforehand.

The team studied how developers had already created their own themes through browser plugins and GitHub repos, noticing significant variation in preferences. "Some people like very close to pure black dark theme and some people liked more of a lower contrast dimmed theme," she notes. They designed a default dark mode that struck a balance between these preferences while preparing to quickly add variations based on user response.

The launch was successful, with the default dark theme remaining the most popular option years later. About 20% of users preferred the dimmed theme, validating their decision to offer multiple options. "Focusing on outcomes not output is the key thing," Mounter emphasizes. "When you're beginning a project you should be clear on what are the outcomes you're hoping to seek."

Designing for the AI Era: Core Skills That Endure

Mounter believes that working in tech requires embracing constant change, especially with the rise of generative AI. "New technologies come out all the time. There's just sometimes some bigger steps and bigger moments like we're having right now."

She advises designers to remember that core skills remain essential: "Building empathy for the customer experience, being good at storytelling and communicating ideas, being creative and knowing how to get from a blank page or an ambiguous problem to something that is a great solution."

Technical comfort is increasingly important: "As a designer, you more or less have to use the same tools that engineers do. So being comfortable with code, being comfortable with working with new technologies is going to give you a leg up in terms of designing for AI experiences."