How to change the ChatGPT theme

Appearance is stored per device, so changing it on the web does not change the mobile app.

Accent color is on the same General page. It tints message bubbles, buttons and highlighted text, and unlike Appearance it is saved to your account, so it syncs between devices.

OpenAI lists Blue, Green, Yellow, Pink, Orange and Purple, plus a neutral that shows as Black in light mode and White in dark mode. Some accounts also see Default, and the exact list can vary by plan, app version and rollout. There is no custom colour picker and no separate colour for message bubbles.

The Contrast setting (System, Medium, Increased) is available on the web and in the Windows app. It mostly affects light appearance and is separate from dark mode.

There is no built-in setting for fonts, background colours or images, custom colour palettes, or bubble shapes. Text size can only be changed in the Windows app; on the web, use browser zoom (Ctrl or Cmd with + and −).

Hand-written CSS through a userstyle manager like Stylus works, but those styles target ChatGPT's class names and tend to break whenever the site is updated.

ChatTheme is a free Chrome extension that restyles the whole of chatgpt.com: colours, font, corner shape, background and even a frame around the app, from a Windows 95 window to a flip phone. You can also describe a look (“lilac 2004 phone with stickers”) and AI builds it in seconds.

It only changes the look. Every ChatGPT feature keeps working, text contrast is kept at 4.5:1 or better, and Alt+Shift+T switches it off instantly. Small site adapters absorb ChatGPT redesigns, so themes don't break when the site changes.