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React CSS

bello profile image Bello Updated on ・5 min read
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Styles can be applied to a component from an external CSS file. The Person/Person.js file is such an external file.

Webpack is the package responsible for the handling of files. For example with the webpack-babel configuration, not only can we use the ES6+ syntax to import or export JavaScript files (Babel), we can also import CSS file(s), Person/Person.js into a JavaScript file, App.js (Webpack).

Let's style the components below with CSS:

App.js

import React from 'react';
import { useState } from 'react';
import Person from './Person/Person';

const App = () => {
  const [state, setState] = useState({
    persons: {
      name: 'Bello',
      language: 'React',
      id: '2sdr3'
    }
  });

  const personNameHandler = () => {
    setState({
      persons: {
        name: 'Andela',
        language: 'React',
        id: '2sdr3'
      }
    })
  };

  return (
    <div>
      <Person
        name={state.persons.name}
        language={state.persons.language}
        id={state.persons.id} />
      <button
        onClick={personNameHandler}>Change Person State</button>
    </div>
  );
};

export default App;
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Person/Person.js

import React from 'react';
import './Person.css';

const Person = props => {
    return (
        <div className="Person">
            <h3>Name: {props.name}</h3>
            <h3>Skill: {props.language}</h3>
            <h3>ID: {props.id}</h3>
        </div>
    );
};

export default Person;
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External-Internal CSS

CSS rules are globally scoped on components even when written in a separate or external file.

See the example below:

Person/Person.css

.Person {
    margin: 20px auto;
    padding: 5px;
    border: 1px solid #ccc;
    border-radius: 4px;
    line-height: 1.7;
    width: 12.375rem;
    font-family: 'Roboto', sans-serif;
    background-color: white;
}
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Let's import Google Font into index.css.

index.css

@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@300&display=swap');

*, 
*::before,
*::after {
    box-sizing: border-box;
}

html,
body {
    padding: 0;
    margin: 0;
}

body {
    background-color: #f0f0f0;
}
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You may wish to delete the App.css file.

Note: When you inspect the imported CSS font @import url('https://...');, it's in a separate <style> element. This is done automatically by webpack.

Use shortcut key, Ctrl + Shift + ' to open the developer tools. Inspect the Person component. Do you notice any auto-prefix? If yes, it means you are either using an older Chrome, Firefox, or Safari version browser (or any other browser that uses their engine). If No, it means your browser can do without the auto-prefix but renders the right styling on the element. This is possible because it's configured in your package.json or in any other file.

package.json

"browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  }
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Also, since these CSS files are imported into the JavaScript file by the webpack management system, it's intuitive to expect that the stying is globally scoped. That is the CSS rules are injected in the style element.

In the <head> element look for the <style> elements. There are 4 style elements in the index.html file. That is, they all globally scoped in the index.html.

For example, the Person/Person.css CSS rules are injected in the <style> element of the index.html file.

index.html

<style>
.Person {
    margin: 20px auto;
    padding: 5px;
    border: 1px solid #ccc;
    border-radius: 4px;
    line-height: 1.7;
    width: 12.375rem;
    font-family: 'Roboto', sans-serif;
}
</style>
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The sourceMappingURL data warning disappears because styling is applied to components or elements.

Inline CSS

If a React element needs styling, there's no need to write the rules in a separate file or globally. React elements can be styled inline but not in CSS format but JavaScript syntax.

In the example below the name, styleButton is an object. The property names of the object are written in camelCase when necessary.

Let's style the button element:

App.js

import React from 'react';
import { useState } from 'react';
import Person from './Person/Person';

const App = () => {
  const [state, setState] = useState({
    persons: {
      name: 'Bello',
      language: 'React',
      id: '2sdr3'
    }
  });

  const personNameHandler = () => {
    setState({
      persons: {
        name: 'Andela',
        language: 'React',
        id: '2sdr3'
      }
    })
  };

  const styleButton = {
    border: '1px solid black',
    borderRadius: '4px',
    backgroundColor: 'blueviolet',
    color: 'white',
    display: 'block',
    margin: '0 auto',
    padding: '10px',
    cursor: 'pointer'
  }

  return (
    <div>
      <Person
        name={state.persons.name}
        language={state.persons.language}
        id={state.persons.id} />
      <button
        style={styleButton}
        onClick={personNameHandler}>Change Person State</button>
    </div>
  );
};

export default App;
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As you can see above, the style attribute, style is in-line with the <button> element - style={styleButton}.

An alternative syntax is shown below - style={{...}} syntax:

App.js

import React from 'react';
import { useState } from 'react';
import Person from './Person/Person';

const App = () => {
  const [state, setState] = useState({
    persons: {
      name: 'Bello',
      language: 'React',
      id: '2sdr3'
    }
  });

  const personNameHandler = () => {
    setState({
      persons: {
        name: 'Andela',
        language: 'React',
        id: '2sdr3'
      }
    })
  };

  return (
    <div>
      <Person
        name={state.persons.name}
        language={state.persons.language}
        id={state.persons.id} />
      <button
        style={{
          border: '1px solid black',
          borderRadius: '4px',
          backgroundColor: 'blueviolet',
          color: 'white',
          display: 'block',
          margin: '0 auto',
          padding: '10px',
          cursor: 'pointer'
        }}
        onClick={personNameHandler}>Change Person State</button>
    </div>
  );
};

export default App;
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CSS Module

CSS module is an alternative way to add CSS to your app. It allows you to import your CSS module in a script file.

Let's center the body of the App.js component:

body.module.css

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

button {
    border: 1px solid #000;
    border-radius: 4px;
    background-color: blueviolet;
    color: white;
    display: block;
    margin: 0 auto;
    padding: 10px;
    cursor: pointer
}
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Note: The CSS module allows JavaScript file to import the .module.css file for styling in a component or on an element. The syntax is filename.module.css. Where .module.css is the extension The added advantage is you do not have to worry about name conflicts.

App.js

import React from 'react';
import { useState } from 'react';
import Person from './Person/Person';
import bodyStyles from './body.module.css';

const App = () => {
  const [state, setState] = useState({
    persons: {
      name: 'Bello',
      language: 'React',
      id: '2sdr3'
    }
  });

  const personNameHandler = () => {
    setState({
      persons: {
        name: 'Andela',
        language: 'React',
        id: '2sdr3'
      }
    })
  };

  return (
    <div className={bodyStyles}>
      <Person
        name={state.persons.name}
        language={state.persons.language}
        id={state.persons.id} />
      <button
        onClick={personNameHandler}>Change Person State</button>
    </div>
  );
};

export default App;
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You can be more specific by using the . notation to style a specific element. The className={bodyStyles.button} attribute is added to the button element.

import React from 'react';
import { useState } from 'react';
import Person from './Person/Person';
import bodyStyles from './body.module.css';

const App = () => {
  const [state, setState] = useState({
    persons: {
      name: 'Bello',
      language: 'React',
      id: '2sdr3'
    }
  });

  const personNameHandler = () => {
    setState({
      persons: {
        name: 'Andela',
        language: 'React',
        id: '2sdr3'
      }
    })
  };

  return (
    <div className={bodyStyles.body}>
      <Person
        name={state.persons.name}
        language={state.persons.language}
        id={state.persons.id} />
      <button className={bodyStyles.button}
        onClick={personNameHandler}>Change Person State</button>
    </div>
  );
};

export default App;
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Happy Coding!!!

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