@mui/material/styles/createTypography.js

import deepmerge from '@mui/utils/deepmerge';
function round(value) {
  return Math.round(value * 1e5) / 1e5;
}
const caseAllCaps = {
  textTransform: 'uppercase'
};
const defaultFontFamily = '"Roboto", "Helvetica", "Arial", sans-serif';

/**
 * @see @link{https://m2.material.io/design/typography/the-type-system.html}
 * @see @link{https://m2.material.io/design/typography/understanding-typography.html}
 */
export default function createTypography(palette, typography) {
  const {
    fontFamily = defaultFontFamily,
    // The default font size of the Material Specification.
    fontSize = 14,
    // px
    fontWeightLight = 300,
    fontWeightRegular = 400,
    fontWeightMedium = 500,
    fontWeightBold = 700,
    // Tell MUI what's the font-size on the html element.
    // 16px is the default font-size used by browsers.
    htmlFontSize = 16,
    // Apply the CSS properties to all the variants.
    allVariants,
    pxToRem: pxToRem2,
    ...other
  } = typeof typography === 'function' ? typography(palette) : typography;
  if (process.env.NODE_ENV !== 'production') {
    if (typeof fontSize !== 'number') {
      console.error('MUI: `fontSize` is required to be a number.');
    }
    if (typeof htmlFontSize !== 'number') {
      console.error('MUI: `htmlFontSize` is required to be a number.');
    }
  }
  const coef = fontSize / 14;
  const pxToRem = pxToRem2 || (size => `${size / htmlFontSize * coef}rem`);
  const buildVariant = (fontWeight, size, lineHeight, letterSpacing, casing) => ({
    fontFamily,
    fontWeight,
    fontSize: pxToRem(size),
    // Unitless following https://meyerweb.com/eric/thoughts/2006/02/08/unitless-line-heights/
    lineHeight,
    // The letter spacing was designed for the Roboto font-family. Using the same letter-spacing
    // across font-families can cause issues with the kerning.
    ...(fontFamily === defaultFontFamily ? {
      letterSpacing: `${round(letterSpacing / size)}em`
    } : {}),
    ...casing,
    ...allVariants
  });
  const variants = {
    h1: buildVariant(fontWeightLight, 96, 1.167, -1.5),
    h2: buildVariant(fontWeightLight, 60, 1.2, -0.5),
    h3: buildVariant(fontWeightRegular, 48, 1.167, 0),
    h4: buildVariant(fontWeightRegular, 34, 1.235, 0.25),
    h5: buildVariant(fontWeightRegular, 24, 1.334, 0),
    h6: buildVariant(fontWeightMedium, 20, 1.6, 0.15),
    subtitle1: buildVariant(fontWeightRegular, 16, 1.75, 0.15),
    subtitle2: buildVariant(fontWeightMedium, 14, 1.57, 0.1),
    body1: buildVariant(fontWeightRegular, 16, 1.5, 0.15),
    body2: buildVariant(fontWeightRegular, 14, 1.43, 0.15),
    button: buildVariant(fontWeightMedium, 14, 1.75, 0.4, caseAllCaps),
    caption: buildVariant(fontWeightRegular, 12, 1.66, 0.4),
    overline: buildVariant(fontWeightRegular, 12, 2.66, 1, caseAllCaps),
    // TODO v6: Remove handling of 'inherit' variant from the theme as it is already handled in Material UI's Typography component. Also, remember to remove the associated types.
    inherit: {
      fontFamily: 'inherit',
      fontWeight: 'inherit',
      fontSize: 'inherit',
      lineHeight: 'inherit',
      letterSpacing: 'inherit'
    }
  };
  return deepmerge({
    htmlFontSize,
    pxToRem,
    fontFamily,
    fontSize,
    fontWeightLight,
    fontWeightRegular,
    fontWeightMedium,
    fontWeightBold,
    ...variants
  }, other, {
    clone: false // No need to clone deep
  });
}