Inline CSS

Automatically inline CSS from <style> tags in your HTML emails.

CSS inlining is still important in HTML email, mainly because of Outlook on Windows, which doesn't support multiple classes on elements.

It can also help preserve a decent layout in email clients that do not support embedded CSS (in <style> tags), or when an email is forwarded.

The utility-first approach in Tailwind CSS works great with CSS inlining: utility classes are not 'global', so you won't end up with a font-family inlined on every element (unless you really, really want to).

Usage

To enable CSS inlining, simply set css.inline to true in your config:

export default {
  css: {
    inline: true,
  }
}

Customization

If you need control over how your CSS is inlined, you may pass a configuration object to inlineCSS. Doing this in your Environment config.js will enable CSS inlining for all Templates when building for that Environment.

styleToAttribute

Type: Object
Default: {}

Defines which CSS properties should be duplicated as what HTML attributes.

For example, this property-attribute assignment:

export default {
  inlineCSS: {
    styleToAttribute: {
      'background-color': 'bgcolor',
    }
  }
}

... will transform this:

<table class="bg-slate-300">
  <tr>
    <td>...</td>
  </tr>
</table>

... into this:

<table bgcolor="#cbd5e1" style="background-color: #cbd5e1">
  <tr>
    <td>...</td>
  </tr>
</table>

The available mappings are:

attributeToStyle

Type: Boolean|String[]
Default: undefined

Duplicates specified HTML attributes as inline CSS.

See the documentation here.

applyWidthAttributes

Type: Boolean
Default: true

Whether to use any CSS pixel widths to create width attributes on elements set in css.inline.widthElements.

Set it to false to prevent any width attributes from being added based on inline CSS width:

export default {
  css: {
    inline: {
      applyWidthAttributes: false,
    }
  }
}

widthElements

Type: String[]
Default: ['img', 'video']

Array of HTML elements that can receive width attributes based on inline CSS width.

export default {
  css: {
    inline: {
      widthElements: ['table', 'td', 'th'],
    }
  }
}

applyHeightAttributes

Type: Boolean
Default: true

Whether to use any CSS pixel heights to create height attributes on elements set in css.inline.heightElements.

Set it to false to prevent any height attributes from being added based on inline CSS height:

export default {
  css: {
    inline: {
      applyHeightAttributes: false,
    }
  }
}

heightElements

Type: String[]
Default: ['img', 'video']

Array of HTML elements that can receive height attributes based on inline CSS height.

export default {
  css: {
    inline: {
      heightElements: ['table', 'td', 'th'],
    }
  }
}

excludedProperties

Type: String[]
Default: []

Array of CSS property names that should be excluded from the CSS inlining process.

Names are considered unique, so you will need to specify each one you'd like to exclude.

For example:

export default {
  css: {
    inline: {
      excludedProperties: ['padding', 'padding-left'],
    }
  }
}

codeBlocks

Type: Object
Default: { EJS: {}, HBS: {} }

An object where each value has a start and end to specify fenced code blocks that should be ignored during CSS inlining.

By default, EJS and HBS code blocks are ignored:

{
  EJS: { start: '<%', end: '%>' },
  HBS: { start: '{{', end: '}}' },
}

removeInlinedSelectors

Type: Boolean
Default: true

When css.inline is enabled, classes will be removed from the class attribute of a tag after they have been successfully inlined.

Set this option to false to preserve the classes in the class attribute.

export default {
  css: {
    inline: {
      removeInlinedSelectors: false,
    }
  }
}

resolveCSSVariables

Type: Boolean
Default: true

Whether to resolve CSS variables to their actual values in the inlined CSS.

By default, something like this:

<style>
  :root {
    --color: red;
  }
  .text-red { color: var(--color); }
</style>

<div class="text-red">Hello</div>

... will be inlined as:

<div style="color: red">Hello</div>

If you prefer to keep CSS variables when inlining, set this option to false:

export default {
  css: {
    inline: {
      resolveCSSVariables: false,
    }
  }
}

resolveCalc

Type: Boolean
Default: true

Whether to resolve calc() expressions in the inlined CSS.

By default, something like this:

<style>
  div {
    width: calc(100% / 3);
  }
</style>

<div>Hello</div>

... will be inlined as:

<div style="width: 33.33%">Hello</div>

preferUnitlessValues

Type: Boolean
Default: true

When inlining CSS, 0 values will be inlined without units.

For example, margin: 0px will be inlined as margin: 0.

Set this to false to keep units on 0 values.

export default {
  css: {
    inline: {
      preferUnitlessValues: false,
    }
  }
}

useAttributeSizes

Type: Boolean
Default: undefined

Prefer HTML width and height attributes over inline CSS.

Useful for retina images in Outlook on Windows, which doesn't respect CSS sizes and will render the image in its natural size.

Set this to true to use HTML attributes for sizes instead of inline CSS:

export default {
  css: {
    inline: {
      useAttributeSizes: true,
    }
  }
}

safelist

Type: String[]

An array of strings representing CSS selectors that should not be removed after inlining.

These can be substring matches, so you can use text-red to preserve .text-red, .text-red-500, etc.

export default {
  css: {
    inline: {
      safelist: ['text-red', '.bg-blue-500'],
    }
  }
}

Prevent inlining

You may add an attribute on a <style> tag to prevent Juice from inlining the CSS inside it. Useful for writing email client CSS hacks, or for preserving CSS comments when using the removeCSSComments: false Cleanup option.

<style data-embed>
  /* This CSS will not be inlined */
  .text-red { color: red; }
</style>

Maizzle supports the following attributes for this purpose:

• data-embed
• no-inline
• embed

API

You can use the inlineCSS function to inline CSS in a string of HTML.

Your HTML string will need to have at least one <style> tag in the <head>. Alternatively, you may pass your own CSS to inline through the customCSS option.

Additionally, you may configure the Juice library by passing options in the same object.

import { inlineCSS } from '@maizzle/framework'

const config = {
  customCSS: 'body { background-color: #f8f9fa; }',
  excludedProperties: ['padding', 'padding-left'] // Juice option
}

const html = await inlineCSS('html string', config)