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Applying correctly className with Styled components

2020-11-05 by Nicolas Zozol

Styled component is a technology that scales css. It's great, but there are some traps. Here is what I wished I knew the most when starting Styled Components.

Goals and Difficulties

Styled Component is a library coded by the impressive Max Stoiber and now maintained by many others, proof of success and durability.

There are two main goals in my point of vue.

  • Scale by avoiding hell of BEM, like using class name such as search-box__btn search -box__btn_max_visible
  • Protect your component from the cascading pattern of CSS. Yes. Break the C of CSS

Like you may expect, this second goal may bring some pain, or at least surprises when, like me , your are too naive.

Quick example

Let starts with an example from the doc:

const Button = styled.button`
  color: palevioletred;

const TomatoButton = styled(Button)`
  color: tomato;

That works and gives two nice buttons. But using:

const MyButton = ()=><button>Click Me</button>

const MyTomatoButton = styled(MyButton)`
  color: tomato;

I'm naive and I have a button. I want to style it, so I write styled(button). But my new button won't have any tomato color 😞

Read the manual

First, be smarter than me and don't miss this most important line from the manual:

The styled method works perfectly on all of your own or any third-party component, as long as they attach the passed className prop to a DOM element.

const Link = ({ className, children }) => (
  <a className={className}>

Why ? Because later the examples given across the web, including Styled Component documentation gives examples where it looks easy to modify a component, when this second goal is exactly to avoid any modification of a component.

Applying classes

The problem is that styled(Comp) is effective only if Comp is already a styled component. To achieve this, you must add the className to MyButton

const MyStyledButton = ({className})=><button className={className}>Click Me</button>

const MyTomatoButton = styled(MyStyledButton)`
  color: tomato;

Now StyleComponent will create some classes and apply them to your component, making it a styled component.

ClassName applied to styled component

No className, no style. When using styled.div, then StyledComponent has already applied the className trick.

This is wanted behaviour. You are not supposed to transform a component except if the component creator has explicitly said you can ! It's the open/close principal applied to styling.

Advanced usage


Once a component is styled, you can re-style it.

const AttachingComp = ({className})=><div className={className}>I am a <strong>attaching</strong> component</div>

const GreenAttachingComp= styled(AttachingComp)`

const Child = styled(GreenAttachingComp)`
   margin: 20px 20px;
   color: red;

Restyling from another component

Nesting components

The same closed by default behaviour is applied to nesting components. If you have not applied className to a React element, nesting rules are ...not applied.

const BasicComp = () => <div>I am a <strong>basic </strong>component</div>;

const AttachedComp = ({ className }) => (
  <div className={className}>
    I am an <strong>attached</strong> component

const StyledBasicComp = styled(BasicComp)``;
const StyledAttachedComp = styled(AttachedComp)``;

const DemoNesting = ({className})=>{
  return (
    <div className={className}>

export const StyledDemoNesting = styled(DemoNesting)`
// general css rules. Will be applied to all nodes below

// component rule on basic component. Won't be effective

// component rule on className attached component. Rule is effective

You can test it in this Stackblitz

When should I attach className ?

Most often, you should not. Because it's designed this way. If you have a few rules, you should prefer standard css or sass.

If you have a bigger application, then attaching className could increase interferences.

If you want to present a component in different way, you will rather use a theme or passed props if it's through your application state:

Attaching className is really meant for the case where you create a third party library, and you design a point of extension. You create some open explicitly for the style. Attaching the className will avoid some hacks are they are described here in this issue

I kind of attach className for creating my own library. I design some Theme Component, such as TCard, then I modify the spacing at different point of this Gatsby website, or reuse it for similar websites.

For the moment, it's just a test, and it looks good. But it took me way too much time to really understand how and why attach className. Maybe this article will help you 😊

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