Bootstrap theme editor

Component classes, no build step needed: the widest-installed CSS framework there is. UISandbox builds Bootstrap 5.3.8 from its own package and opens it in the editor: seven screens in Bootstrap's own components and its own defaults. Turn the brand, the type, the spacing and the corners, and every component follows. Nothing to install, nothing uploaded.

Open Bootstrap in the editor Try it on your own app

Bootstrap in the UISandbox editor: the knobs on the left, Bootstrap's own components on the right — Bootstrap as it ships, in the editor. A real screenshot.

What is read from Bootstrap

Version: 5.3.8
Licence: MIT
Package: bootstrap
Runs in: any page, no framework asked
Variables: 117 in its light mode, and its own dark mode, read from its package
Brand as it ships: #0d6efd
Body type: the system stack
Corners: 6px

What you take with you

Export writes Bootstrap's design system in Bootstrap's own names, starting from what you see:

_custom.scss: Bootstrap's Sass entry, for the brand it compiles in
theme.css: the variables, in Bootstrap's own names, as the knobs left them
install.md: where each file goes, step by step
MANIFEST.md: what could not be done, said rather than substituted
DESIGN.md: the design system for people and agents: colours, type, spacing, what each is for
.claude/skills/design-system/SKILL.md: for Claude Code, Cursor or Codex: build the next screen in Bootstrap's own classes
tokens.json: W3C design tokens, which Tokens Studio and Figma variables import

On your own app

If your app runs on Bootstrap, the sandbox recognises it from the rendered page and writes the design system in Bootstrap's names from your app's own values. What you turned on the kit comes with you. The quickest way in is the one where nothing leaves your machine: run npx uisandbox-mcp open in your project, or ask your agent to "open this app in UISandbox". How it works.