Astro 3 supports a brand new light theme along with the original and default dark theme.

theme light ui

theme light ui

Example of a light theme Astro application

When to Use Light vs Dark

It is important to determine the users’ environment and select the appropriate theme. In low-light operating environments where users’ pupils expand to allow more light to enter the cornea, a light-themed UI can be glaring and cause eye strain. Conversely, in a bright operating environment where the pupil contracts, letting less light in, dark-themed UIs can lose distinction and readability.

Light Theme Use Cases:

  • Outdoor environments
  • Brightly lit operating environments
  • Elements with long passages of text

Dark Theme Use Cases

  • Dark operating environments
  • Projection on large screens
  • Applications where a primary media element demands attention

theme darkui 2

theme darkui 2

The Global Status Bar is always rendered with the dark theme, as is any element contained within it.

Mixed Use

Individual sections or components can override their inherited theme on a case-by-case basis, enabling the render an element with a light theme in an predominantly dark-themed interface and vice versa. Examples:

  • Dark-themed elements in the global status bar
  • Light-themed modal window in a dark themed app

theme darkui mixed 3

theme darkui mixed 3

Example of a predominantly dark theme interface with the modal window rendered using the light theme to place greater emphasis on an interaction demanding the user’s attention

Future Considerations

While not enabled by default at this time, light and dark themes can be swapped at runtime. For situations where lighting conditions can vary considerably, consider enabling runtime theme switching. A user-definable toggle in the application settings, an ambient light sensor or respecting OS level dark/light theme settings are all viable options.


Astro applications using the Astro CSS Library will default to the dark theme with no additional involvement by the developer. To enable the light theme with the Astro CSS Library, the <body> element of the application should be given a light-theme class (e.g., <body class=“light-theme”>. For all other applications, refer to the Color Palettes for specific hex/rgb values in light and dark UIs.