bloodTheme.js

function bloodTheme(originalTheme) {
  const originalStylesheet = originalTheme.createStylesheet()
  
  originalTheme.createStylesheet = function() {
    return {
      name: 'blood',
      ...originalStylesheet,
      header: {
        ...originalStylesheet.header,
        color: '#fff',
        fontStyle: 'italic',
      },
      background: {
        ...originalStylesheet.background,
        color: '#fff',
        backgroundColor: '#C53719',
      },
      button: {
        ...originalStylesheet.button,
        backgroundColor: 'maroon',
        color: '#fff',
      },
      primary: '#C53719',
      secondary: 'maroon',
      textColor: '#fff',
    }
  }
}