Styling React Components

Recall: We know 2 ways to style components and elements so far.

1. Inline styling using style object passed into component as style={style}

• Specific to component

• But can't apply pseudo-selectors like hover or media queries

1. Stylesheet import using import ./style.css" that gets compiled by Webpack

• Styles will apply globally

Note: To add media queries and pseudo-selectors to inline styles, install the popular package Radium.

• For pseudo-selectors, simply wrap your component inside Radium class when you export component.

• For media queries, simply wrap your App return statement with StyleRoot component.

Setting Styles Dynamically

To set inline styles dynamically, you can just update the style object!

render() {
  const style = {
    color: blue
  };

  if (this.state.isOff) style.color = "gray";

  return <div style={style}>Hi!</div>;
};

To set classes dynamically, just use an array with the join() method.

render() {
  const classes = [];

  if (this.state.persons.length < 3) {
    classes.push("red");
    // classes = ["red"]
  };
  if (this.state.persons.length < 2) {
    classes.push("bold");
    // classes = ["red", "bold"]
  };

  return <div className={classes.join(" ")}>Hi!</div>;
};

Scoping Styles with CSS Modules

CSS modules allow you to scope styles in a *.module.css file to a specific component, even if those styles would override other stylesheets (e.g. using same class name).

As of react-scripts@2.0.0 and higher, CSS modules are supported. To make them work in prior versions, you need to manually configure the Webpack config:

1. npm run eject to remove react-scripts and give you full access to Webpack config (as opposed to react-scripts managing it for you).

2. Update webpack.config.dev.js and webpack.config.prod.js files in new config folder to turn on CSS modules.

• Note: This works because you're telling Webpack how to bundle the CSS

1. In the Component.js file, import classes from "./Component.css" to get access to a classes object.

2. Go to the appropriate element in the return statement and add className={classes.className} (where className is found in your Component.css file).

CSS modules scope your CSS because when Webpack bundles your files, it takes your class names and appends component names and unique hashes like [name]__[local]__[hash]. Then it exposes a JS object that maps your class names to their appended versions using key/value pairs of the form className: [name]__[local]__[hash]. You then use this object in your component.

Pro tip: To make a CSS class global, append :global .class { ... }.

Targeting child elements

A component always returns one element with child elements all inside. To target child elements, you can just use this CSS selector syntax: .Parent child. .Parent will be converted into a unique class name, so child will be uniquely targeted!

Note: You can also just give your child elements their own class.

.App { ... }

.App button { /* <-- targets buttons inside .App */
  color: red;
}

Using pseudo-selectors

Simple. Just add the pseudo-selector to selector that includes a class. The class will be converted:

.App button:hover { ... }

Using media queries

Simple again. Just make sure style rules inside your media query make use of classes.

@media (min-width: 480px) {
  .App { ... }
}