feat(BaseStyles): Convert BaseStyles to CSS modules behind team feature flag (#5361)

* Create css modules for BaseStyles

* Convert BaseStyles to CSS modules behind team feature flag

* Add changeset

* Update anchoroverlay snapshot for BaseStyles

* Fix lint

* Fix integration regression

* Update snapshot to remove unnecessary whitespace

---------

Co-authored-by: Jon Rohan <yes@jonrohan.codes>

Author: JelloBagel

.changeset/grumpy-numbers-eat.md

@@ -0,0 +1,5 @@
+---
+"@primer/react": minor
+---
+
+Convert BaseStyles to CSS modules behind team feature flag

packages/react/src/BaseStyles.module.css

@@ -0,0 +1,50 @@
+/* stylelint-disable selector-max-specificity */
+/* stylelint-disable selector-type-no-unknown */
+
+/* -------------------------------- 
+ *           Global Styles         
+ *--------------------------------- */
+* {
+  box-sizing: border-box;
+}
+
+body {
+  margin: 0;
+}
+
+table {
+  /* stylelint-disable-next-line primer/borders */
+  border-collapse: collapse;
+}
+
+[role='button']:focus:not(:focus-visible):not(.focus-visible),
+[role='tabpanel'][tabindex='0']:focus:not(:focus-visible):not(.focus-visible),
+button:focus:not(:focus-visible):not(.focus-visible),
+summary:focus:not(:focus-visible):not(.focus-visible),
+a:focus:not(:focus-visible):not(.focus-visible) {
+  outline: none;
+  box-shadow: none;
+}
+
+[tabindex='0']:focus:not(:focus-visible):not(.focus-visible),
+details-dialog:focus:not(:focus-visible):not(.focus-visible) {
+  outline: none;
+}
+
+/* -------------------------------------------------------------------------- */
+
+.BaseStyles {
+  /* Global styles for light mode */
+  &:has([data-color-mode='light']) {
+    input & {
+      color-scheme: light;
+    }
+  }
+
+  /* Global styles for dark mode */
+  &:has([data-color-mode='dark']) {
+    input & {
+      color-scheme: dark;
+    }
+  }
+}

packages/react/src/BaseStyles.tsx

@@ -1,13 +1,19 @@
 import React from 'react'
+import {clsx} from 'clsx'
 import styled, {createGlobalStyle} from 'styled-components'
+import type {ComponentProps} from './utils/types'
 import type {SystemCommonProps, SystemTypographyProps} from './constants'
 import {COMMON, TYPOGRAPHY} from './constants'
 import {useTheme} from './ThemeProvider'
-import type {ComponentProps} from './utils/types'
+import {useFeatureFlag} from './FeatureFlags'
+import {toggleStyledComponent} from './internal/utils/toggleStyledComponent'
+import classes from './BaseStyles.module.css'
 
 // load polyfill for :focus-visible
 import 'focus-visible'
 
+const CSS_MODULES_FEATURE_FLAG = 'primer_react_css_modules_team'
+
 const GlobalStyle = createGlobalStyle<{colorScheme?: 'light' | 'dark'}>`
   * { box-sizing: border-box; }
   body { margin: 0; }
@@ -29,27 +35,34 @@ const GlobalStyle = createGlobalStyle<{colorScheme?: 'light' | 'dark'}>`
   }
 `
 
-const Base = styled.div<SystemTypographyProps & SystemCommonProps>`
-  ${TYPOGRAPHY};
-  ${COMMON};
-`
+const Base = toggleStyledComponent(
+  CSS_MODULES_FEATURE_FLAG,
+  'div',
+  styled.div<SystemTypographyProps & SystemCommonProps>`
+    ${TYPOGRAPHY};
+    ${COMMON};
+  `,
+)
 
 export type BaseStylesProps = ComponentProps<typeof Base>
 
 function BaseStyles(props: BaseStylesProps) {
-  const {children, color = 'fg.default', fontFamily = 'normal', lineHeight = 'default', ...rest} = props
+  const {children, color = 'fg.default', fontFamily = 'normal', lineHeight = 'default', className, ...rest} = props
 
   const {colorScheme, dayScheme, nightScheme} = useTheme()
+  const enabled = useFeatureFlag(CSS_MODULES_FEATURE_FLAG)
+
+  const stylingProps = enabled ? {className: clsx(classes.BaseStyles, className)} : {className}
 
   /**
    * We need to map valid primer/react color modes onto valid color modes for primer/primitives
    * valid color modes for primer/primitives: auto | light | dark
    * valid color modes for primer/primer: auto | day | night | light | dark
    */
-
   return (
     <Base
       {...rest}
+      {...stylingProps}
       color={color}
       fontFamily={fontFamily}
       lineHeight={lineHeight}
@@ -58,7 +71,7 @@ function BaseStyles(props: BaseStylesProps) {
       data-light-theme={dayScheme}
       data-dark-theme={nightScheme}
     >
-      <GlobalStyle colorScheme={colorScheme?.includes('dark') ? 'dark' : 'light'} />
+      {!enabled && <GlobalStyle colorScheme={colorScheme?.includes('dark') ? 'dark' : 'light'} />}
       {children}
     </Base>
   )

packages/react/src/__tests__/BaseStyles.test.tsx

@@ -30,4 +30,16 @@ describe('BaseStyles', () => {
     const {container} = render(<BaseStyles {...styles}></BaseStyles>)
     expect(container.children[0]).toHaveStyle({color: '#f00', 'font-family': 'Arial', 'line-height': '3.5'})
   })
+
+  it('accepts className and style props', () => {
+    const styles = {
+      style: {margin: '10px'},
+      className: 'test-classname',
+      sx: {},
+    }
+
+    const {container} = render(<BaseStyles {...styles}></BaseStyles>)
+    expect(container.children[0]).toHaveClass('test-classname')
+    expect(container.children[0]).toHaveStyle({margin: '10px'})
+  })
 })