# @fluentui/theme **Basic building blocks for [Fluent UI React](https://developer.microsoft.com/en-us/fluentui) Themes** Define your own theme based on an existing theme: ```js import { createTheme, Theme, FontWeights } from '@fluentui/theme'; export const MyTheme: Theme = createTheme({ components: { Button: { variants: { fontWeight: FontWeights.semibold, paddingLeft: '24px', paddingRight: '24px', }, }, }, }); ```