[Layout foundations] Refactor Box and update Toast to use Box (#7279)

### WHY are these changes introduced?

Resolves #7134.
[Storybook
URL](https://5d559397bae39100201eedc1-bongofonfc.chromatic.com/?path=/story/all-components-toast--default).

An earlier [prototype](#7096)
explored adding `className` support to the `Box` component and keeping
it as an internal component.
This prototype explores keeping `Box` external without the `className`
prop and replacing custom divs in `Toast` with the `Box` component.

Even if we don't update `Toast` yet, there are some commits in this PR
I'd like to keep that cleans up some of the types and prop descriptions
in the `Box` component.

### WHAT is this pull request doing?
- Cleans up types and updates prop descriptions in `Box`
- Adds `color` and `maxWidth` support to `Box`
- Updates `Toast` to use `Box` where custom `div` are being used

    <details>
      <summary>Toast original</summary>
<img
src="https://user-images.githubusercontent.com/26749317/192353275-5ca804db-0873-4e13-9061-59ee13425538.gif"
alt="Toast original">
    </details>
    <details>
      <summary>Toast refactored with Box</summary>
<img
src="https://user-images.githubusercontent.com/26749317/192353264-6eff870c-ddfb-4583-8d57-6a93f15daf94.gif"
alt="Toast refactored with Box">
    </details>

<!-- ℹ️ Delete the following for small / trivial changes -->

### How to 🎩

🖥 [Local development
instructions](https://github.com/Shopify/polaris/blob/main/README.md#local-development)
🗒 [General tophatting
guidelines](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md)
📄 [Changelog
guidelines](https://github.com/Shopify/polaris/blob/main/.github/CONTRIBUTING.md#changelog)

<!--
  Give as much information as needed to experiment with the component
  in the playground.
-->

<details>
<summary>Copy-paste this code in
<code>playground/Playground.tsx</code>:</summary>

```jsx
import React, {useState, useCallback} from 'react';

import {Page, Frame, Toast, Button} from '../src';

export function Playground() {
  const [active, setActive] = useState(false);

  const toggleActive = useCallback(() => setActive((active) => !active), []);

  const toastMarkup = active ? (
    <Toast content="It's toasty" onDismiss={toggleActive} />
  ) : null;

  return (
    <Frame>
      <Page title="Toast example using Box">
        <Button onClick={toggleActive}>Show Toast (with 📦)</Button>
        {toastMarkup}
      </Page>
    </Frame>
  );
}
```

</details>

### 🎩 checklist

- [ ] Tested on
[mobile](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md#cross-browser-testing)
- [ ] Tested on [multiple
browsers](https://help.shopify.com/en/manual/shopify-admin/supported-browsers)
- [ ] Tested for
[accessibility](https://github.com/Shopify/polaris/blob/main/documentation/Accessibility%20testing.md)
- [ ] Updated the component's `README.md` with documentation changes
- [ ] [Tophatted
documentation](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting%20documentation.md)
changes in the style guide

Co-authored-by: Kyle Durand <[email protected]>

Author: laurkim

polaris-react/src/components/Box/Box.scss

@@ -10,10 +10,12 @@
   --pc-box-border-left: initial;
   --pc-box-border-right: initial;
   --pc-box-border-top: initial;
+  --pc-box-color: initial;
   --pc-box-margin-bottom: initial;
   --pc-box-margin-left: initial;
   --pc-box-margin-right: initial;
   --pc-box-margin-top: initial;
+  --pc-box-max-width: initial;
   --pc-box-padding-bottom: initial;
   --pc-box-padding-left: initial;
   --pc-box-padding-right: initial;
@@ -28,10 +30,12 @@
   border-left: var(--pc-box-border-left);
   border-right: var(--pc-box-border-right);
   border-top: var(--pc-box-border-top);
+  color: var(--pc-box-color);
   margin-bottom: var(--pc-box-margin-bottom);
   margin-left: var(--pc-box-margin-left);
   margin-right: var(--pc-box-margin-right);
   margin-top: var(--pc-box-margin-top);
+  max-width: var(--pc-box-max-width);
   padding-bottom: var(--pc-box-padding-bottom);
   padding-left: var(--pc-box-padding-left);
   padding-right: var(--pc-box-padding-right);

polaris-react/src/components/Box/Box.tsx

@@ -5,8 +5,7 @@ import {classNames, sanitizeCustomProperties} from '../../utilities/css';
 
 import styles from './Box.scss';
 
-type ColorsTokenGroup = typeof colors;
-type ColorsTokenName = keyof ColorsTokenGroup;
+type ColorsTokenName = keyof typeof colors;
 export type BackgroundColorTokenScale = Extract<
   ColorsTokenName,
   | 'background'
@@ -15,23 +14,20 @@ export type BackgroundColorTokenScale = Extract<
   | `surface-${string}`
   | 'backdrop'
   | 'overlay'
+  | `action-${string}`
 >;
+type ColorTokenScale = Extract<ColorsTokenName, 'text' | `text-${string}`>;
 
-type DepthTokenGroup = typeof depth;
-type DepthTokenName = keyof DepthTokenGroup;
+type DepthTokenName = keyof typeof depth;
 type ShadowsTokenName = Exclude<DepthTokenName, `shadows-${string}`>;
-
 export type DepthTokenScale = ShadowsTokenName extends `shadow-${infer Scale}`
   ? Scale
   : never;
 
-type ShapeTokenGroup = typeof shape;
-type ShapeTokenName = keyof ShapeTokenGroup;
-
+type ShapeTokenName = keyof typeof shape;
 type BorderShapeTokenScale = ShapeTokenName extends `border-${infer Scale}`
   ? Scale
   : never;
-
 type BorderTokenScale = Exclude<
   BorderShapeTokenScale,
   `radius-${string}` | `width-${string}`
@@ -58,10 +54,7 @@ interface BorderRadius {
   topRight: BorderRadiusTokenScale;
 }
 
-type SpacingTokenGroup = typeof spacing;
-type SpacingTokenName = keyof SpacingTokenGroup;
-
-// TODO: Bring this logic into tokens
+type SpacingTokenName = keyof typeof spacing;
 export type SpacingTokenScale = SpacingTokenName extends `space-${infer Scale}`
   ? Scale
   : never;
@@ -73,53 +66,60 @@ interface Spacing {
   top: SpacingTokenScale;
 }
 
+type Element = 'div' | 'span';
+
 export interface BoxProps {
-  as?: 'div' | 'span';
-  /** Background color of the Box */
+  /** HTML Element type */
+  as?: Element;
+  /** Background color */
   background?: BackgroundColorTokenScale;
-  /** Border styling of the Box */
+  /** Border style */
   border?: BorderTokenScale;
-  /** Bottom border styling of the Box */
+  /** Bottom border style */
   borderBottom?: BorderTokenScale;
-  /** Left border styling of the Box */
+  /** Left border style */
   borderLeft?: BorderTokenScale;
-  /** Right border styling of the Box */
+  /** Right border style */
   borderRight?: BorderTokenScale;
-  /** Top border styling of the Box */
+  /** Top border style */
   borderTop?: BorderTokenScale;
-  /** Border radius of the Box */
+  /** Border radius */
   borderRadius?: BorderRadiusTokenScale;
-  /** Bottom left border radius of the Box */
+  /** Bottom left border radius */
   borderRadiusBottomLeft?: BorderRadiusTokenScale;
-  /** Bottom right border radius of the Box */
+  /** Bottom right border radius */
   borderRadiusBottomRight?: BorderRadiusTokenScale;
-  /** Top left border radius of the Box */
+  /** Top left border radius */
   borderRadiusTopLeft?: BorderRadiusTokenScale;
-  /** Top right border radius of the Box */
+  /** Top right border radius */
   borderRadiusTopRight?: BorderRadiusTokenScale;
-  /** Inner content of the Box */
+  /** Inner content */
   children: ReactNode;
-  /** Spacing outside of the Box */
+  /** Color of children */
+  color?: ColorTokenScale;
+  /** Spacing outside of container */
   margin?: SpacingTokenScale;
-  /** Bottom spacing outside of the Box */
+  /** Bottom spacing outside of container */
   marginBottom?: SpacingTokenScale;
-  /** Left side spacing outside of the Box */
+  /** Left spacing outside of container */
   marginLeft?: SpacingTokenScale;
-  /** Right side spacing outside of the Box */
+  /** Right spacing outside of container */
   marginRight?: SpacingTokenScale;
-  /** Top spacing outside of the Box */
+  /** Top spacing outside of container */
   marginTop?: SpacingTokenScale;
-  /** Spacing inside of the Box */
+  /** Maximum width of container */
+  maxWidth?: string;
+  /** Spacing around children */
   padding?: SpacingTokenScale;
-  /** Bottom spacing inside of the Box */
+  /** Bottom spacing around children */
   paddingBottom?: SpacingTokenScale;
-  /** Left side spacing inside of the Box */
+  /** Left spacing around children */
   paddingLeft?: SpacingTokenScale;
-  /** Right side spacing inside of the Box */
+  /** Right spacing around children */
   paddingRight?: SpacingTokenScale;
-  /** Top spacing inside of the Box */
+  /** Top spacing around children */
   paddingTop?: SpacingTokenScale;
-  /** Shadow on the Box */
+  /** Shadow */
   shadow?: DepthTokenScale;
 }
 
@@ -139,11 +139,13 @@ export const Box = forwardRef<HTMLElement, BoxProps>(
       borderRadiusTopLeft,
       borderRadiusTopRight,
       children,
+      color,
       margin,
       marginBottom,
       marginLeft,
       marginRight,
       marginTop,
+      maxWidth,
       padding,
       paddingBottom,
       paddingLeft,
@@ -221,6 +223,7 @@ export const Box = forwardRef<HTMLElement, BoxProps>(
             '--pc-box-border-radius-top-right': `var(--p-border-radius-${borderRadiuses.topRight})`,
           }
         : undefined),
+      ...(color ? {'--pc-box-color': `var(--p-${color})`} : undefined),
       ...(margins.bottom
         ? {'--pc-box-margin-bottom': `var(--p-space-${margins.bottom})`}
         : undefined),
@@ -233,6 +236,7 @@ export const Box = forwardRef<HTMLElement, BoxProps>(
       ...(margins.top
         ? {'--pc-box-margin-top': `var(--p-space-${margins.top})`}
         : undefined),
+      ...(maxWidth ? {'--pc-box-max-width': `${maxWidth}px`} : undefined),
       ...(paddings.bottom
         ? {'--pc-box-padding-bottom': `var(--p-space-${paddings.bottom})`}
         : undefined),
@@ -256,8 +260,8 @@ export const Box = forwardRef<HTMLElement, BoxProps>(
       as,
       {
         className,
-        style: sanitizeCustomProperties(style),
         ref,
+        style: sanitizeCustomProperties(style),
       },
       children,
     );