In regular JavaScript, style names are written in hyphenated-lowercase:

const styles = {
  'margin-top': '20px',
  'background-color': 'green'
};

In React, those same names are instead written in camelCase:

const styles = {
  marginTop: '20px',
  backgroundColor: 'green'
};

This has zero effect on style property values, only on style property names.