message: docs(readme): add styling section
diff: @@ -8,6 +8,7 @@ React Flow is a library for building node-based graphs. You can easily implement
  - [Installation](#installation)
  - [Usage](#usage)
  - [ReactFlow Component Props](#reactflow-component-props)
  +- [Styling](#styling)
  - [Nodes](#nodes)
  - [Props](#props-1)
  - [Node Types / Custom Nodes](#node-types--custom-nodes)
  @@ -85,6 +86,34 @@ const BasicGraph = () => (
  - `onlyRenderVisibleNodes`: default: `true`
  - `isInteractive`: default: `true`. If the graph is not interactive you can't drag any nodes
  +## Styling
  +
  +There are two ways how you can style the graph and the elements.
  +You can create your own CSS rules or pass style properties to the components.
  +
  +#### Using classnames
  +
  +Since we are using DOM nodes for rendering the chart you can simply overwrite the styles with your own CSS rules.
  +The React Flow wrapper has the className `react-flow`. So if you want to change the graph background for example you can do:
  +
  +```css
  +.react-flow {
  + background: red;
  +}
  +```
  +
  +The same applies to the nodes (className: `react-flow__node`) and edges (className: `react-flow__edge`).
  +
  +
  +#### Using properties
  +
  +You could achieve the same effect by passing a style prop to the React Flow component:
  +
  +```
  +<ReactFlow elements={element} style={{ background: 'red', width: '100%' height: '300px' }}/>
  +```
  +
  +
  ## Nodes
  There are three different [node types](#node-types--custom-nodes) (`default`, `input`, `output`) you can use. You can also create [custom nodes](#node-types--custom-nodes).
  