README

12px vertical rhythm with correctly aligned baselines

Styled Components Rhythm

Beautifully aligned type with Styled Components

Installation

npm i @ceteio/styled-components-rhythm

or, with yarn:

yarn add @ceteio/styled-components-rhythm

Usage

import { ThemeProvider, injectGLobal }, styled from 'styled-components';
import styledComponentsRhythm from '@ceteio/styled-components-rhythm';

const rhythm = styledComponentsRhythm({
  baseFontSize: 1, // 1rem. Browser default makes this 16px
  baseLineHeight: 1.2, // unitless line-height, see: https://css-tricks.com/almanac/properties/l/line-height/#comment-1587658
  rhythmHeight: 0.75, // rem units. With browser default, this is 16px * 0.75rem == 12px
  capHeights: {
    // Calculated with https://codepen.io/sebdesign/pen/EKmbGL?editors=0011
    Lato: 0.72,
  },
  debug: true,
});

injectGLobal`
  /* Reset global margins and padding */
  h1, p {
    margin: 0;
    padding: 0;
  }

  /* Using Lato font https://fonts.google.com/specimen/Lato */
  @import url('https://fonts.googleapis.com/css?family=Lato')

  ${rhythm.global()}
`;

const H1 = styled.h1`
  ${props => props.theme.setFontWithRhythm('Lato', 3)}
  margin-top: ${props => props.theme.rhythmSizing(3)}rem;
`;

const Paragraph = styled.p`
  ${props => props.theme.setFontWithRhythm('Lato', 1)}
  margin-top: ${props => props.theme.rhythmSizing(2)}rem;
`;

export default () => (
  <ThemeProvider theme={rhythm.theme}>
    <H1>Hello world</H1>
    <Paragraph>How are you today?</Paragraph>
    <Paragraph>Feeling quite <em>aligned</em>!</Paragraph>
  </ThemeProvider>
);

API

Creating Rhythm

The main export is a function which returns a rhythm object suitable for adding to a Styled Components <ThemeProvider>:

import styledComponentsRhythm from '@ceteio/styled-components-rhythm';

const rhythm = styledComponentsRhythm(options);
// { theme: ..., global: ... }

`options` (`Object`)

baseFontSize (Number): The rem font size of your root element (ie; the <body>).
rhythmHeight (Number): The rem vertical grid size, to which text will have its baseline aligned. Works best when it divides evenly into (baseFontSize * defaultLineHeight).
capHeights (Object): Map of font-family font name -> proportional height of capital letters. Heights can be calculated with this tool. For example:
```
{
  Lato: 0.72,
}
```
defaultLineHeight (Number): Default for setFontWithRhythm() below. Must be a unitless value, which will be relative to the font size of an element.
debug (Boolean): Will inject red horizontal lines to body for visually debugging alignments.
defaultOutputType (String): Set the output type of setFontWithRhythm() & global(). 'string': Return a css string . 'object': Return a css style object. Default: 'string'.

Setting the theme

There are two pieces to the puzzle, both of which must be used to have effective vertical rhythm; rhythm.theme, and rhythm.global:

import styledComponentsRhythm from '@ceteio/styled-components-rhythm';
import { injectGlobal, ThemeProvider } from 'styled-components';

const rhythm = styledComponentsRhythm(options);

injectGlobal`${rhythm.global()}`;
return <ThemeProvider theme={rhythm.theme}>...</ThemeProvider>;

`theme` (`Object`)

Pass this object to a Styled Components ThemeProvider as the theme:

const rhythm = styledComponentsRhythm(options);

return <ThemeProvider theme={rhythm.theme}>...</ThemeProvider>;

`global([outputType]) => String`

A string containing global CSS that needs to be applied. Best done using styled-component's injectGlobal:

const rhythm = styledComponentsRhythm(options);

injectGlobal`${rhythm.global()}`;

or Emotion's <Global> component:

<Global styles={rhythm.global('object')} />

Parameters

outputType (String): 'string': Return a css string. 'object': Return a css style object. Default: the value of defaultOutputType.

Using the theme values

You now have access to the following via the theme prop within a styled component:

`rhythmHeight`

The value as passed when creating the theme object.

`setFontWithRhythm(fontName, fontSizeRem[, desiredLineHeight[, outputType]]) => String`

The main function which will generate the CSS necessary to correctly align the font to a rhythm baseline.

This function makes 2 assumptions:

All previous elements on the page are also correctly aligned to your vertical rhythm.
You will not manually set padding-top or margin-bottom on this element.

Parameters

fontName (String): Should match the font name as you would declare it in the CSS property font-family.
fontSizeRem (Number): A multiple of baseFontSize.
desiredLineHeight (Number): Will be rounded to the nearest rhythm line so you don't have to worry.
outputType (String): 'string': Return a css string. 'object': Return a css style object. Default: the value of defaultOutputType.

The output is the CSS string to add to the component:

const H1 = styled.h1`
  ${props => props.theme.setFontWithRhythm('Lato', 3)}
`;

Or as an object using the css prop (in both Styled Components & Emotion):

const H1 = props => (
  <h1 css={theme => theme.setFontWithRhythm('Lato', 3, 1, 'object')} />
);

`rhythmSizing(multiple) => Number`

A simple helper to calculate multiple * rhythmHeight.

Works great for setting margins or padding:

const H1 = styled.h1`
  margin-top: ${props => props.theme.rhythmSizing(3)}rem;
`;

Related Projects

capsize by Seek: "Using font metadata, text can now be sized according to the height of its capital letters while trimming the space above capital letters and below the baseline."
basekick by Michael Taranto is another implementation of the same thing, targeted at LESS.
https://www.w3.org/TR/css-rhythm-1/ is a proposal to support vertical rhythm directly in CSS.

Usage no npm install needed!