Styling and CSS libraries

Spoiler alert! I will use CSS Modules in this tutorial for the simple reason that a lot of CSS libraries had problems with Server components when some time ago I started to experiment with Next.js 13 and Server components. I did NOT want to add an experimental library to my project, so I started searching for an alternative

Why CSS Modules?

When I started writing this tutorial, CSS Modules were among the few choices that worked well with Next.js 13 and Server Components, so I decided to try it. Some CSS libraries that were very popular did not work with Next.js 13, which is why the Next.js team has put up a Next.js "CSS-in-JS" documentation page that lists those who work with client components, but it doesn't mean they work with server components (actually a lot of them still don't), for more details keep an eye on the Emotion support for App Router Issue #2928) or the styled components for Next.js 13 Issue #3856 if those are libraries you are interested in

I'm glad I chose to use CSS Modules because I rediscovered how enjoyable it can be to write vanilla CSS without having to spend time reading documentation to understand how a certain CSS library works or learning how to do something you know can be done in CSS (but you don't know how to do it with the library you are using).

On the other hand, I indeed spent a lot of time reading MDN documentation about modern CSS features, like using custom properties (CSS variables), native CSS nesting (it is great to see this feature that you might know from pre-processors like SASS coming to CSS, but for this one I decided not to use it yet as it is maybe still a bit early in terms of browsers that support it). I spent time learning about calc() and color-mix() functions, pure CSS on scroll animations and a bunch more, but I feel like it was time well invested.

Feel free to skip the few chapters about styling in this tutorial if you already know CSS Modules, but if you haven't used CSS Modules and want to try out something new (even if it is only to be able to compare it to the solution you usually use), then maybe use this tutorial to get an introduction and then later decide for yourself if you want to continue using CSS Modules for your own project(s)

Why NOT Tailwind?

I'm sorry 😢, I thought about Tailwind but in the end I decided I wanted to use CSS Modules for this tutorial. I wanted to try out CSS Modules to see if writing vanilla CSS in CSS Modules is a good alternative or not. I wanted a powerfull yet simple solution, something that feels like you are actually writing CSS and NOT using some abstraction layer I know.

If you like Tailwind and want to use it with Next.js 13 / 14, the good news is that because Tailwind introduced a new just-in-time (JIT) compiler in version 2.1 and then used JIT by default starting with version 3, Tailwind will not have problems in regards to server components compared to a lot of other CSS libraries that did or still do have problems

So, if you prefer Tailwind, then using Tailwind (instead of the CSS Modules I will use here), is a good alternative

If you want to use a UI library instead, then maybe have a look at Next UI, which is a beautiful UI based on Tailwind CSS

Getting started with CSS Modules

Next.js supports CSS Modules out of the box, which means there is NO need to install any extra packages, and CSS Modules are React Server Components (RSC) compatible, which these days should be a requirement for CSS libraries that you intend to use with Next.js 13 / 14

CSS Modules let you write vanilla CSS in *.module.css files that you then import into your components or pages

Let's start with a simple example: go into the /components/tutorial_examples folder and create a new UI folder

Next, in the UI folder, we create a new button.module.css file and add the following content:

.reset {
    background: none;
    border: none;
    padding: 0;
}

And then we create a second Button.tsx file (also in the UI folder) with the following content:

import styles from './button.module.css'
 
const UIButton: React.FC = (): JSX.Element => {
 
    return (
        <button className={styles.reset}>
            I&apos;m a UI button
        </button>
    )
}
 
export default UIButton

Line 1: we import the CSS module

Line 6: we apply the .reset class we added in our button.module.css CSS module to the button

Then we go into the /app/(tutorial_examples) folder and create a new styling folder

Then, in the styling folder, we create a new page.tsx file and paste the following content into it:

import UIButton from '@/components/tutorial_examples/UI/Button'
 
export default function StylingExamplePage() {
 
    return (
        <>
            <UIButton />
        </>
    )
 
}

Line 1: we import our custom button component that is styled using a CSS module

Line 7: we use the button

There is not much to see yet, but if you want to check out the result, make sure your dev server is running and then in your browser navigate to the styling page at http://localhost:3000/styling

Great 🎉 we already know how to use CSS Modules

CSS Modules features

What I like about CSS Modules is that they are pretty simple, which means you won't spend days reading documentation to understand how they work, yet they have some exciting and powerful features

In this chapter, we will have a look at some of them

A significant advantage of CSS Modules is that you don't have to worry about unique names

The library makes them unique for you by adding a hash to the name, meaning you can have two classes named button in two different files, as they are component scoped by default, they will be unique after compilation. The disadvantage with CSS Modules is that when you look at the name using the developer tools, the class and animation names won't be precisely what you have defined, instead the format for names will be: [filename]_[classname]__[hash], so they will still be recognizable but NOT exactly the same. If you don't want the CSS modules to create unique class names for you, you have the option to set a stable class name.

Make sure your dev server is running and then in your browser navigate to the styling page at http://localhost:3000/styling

Then right-click, choose Inspect or press F12 to open the dev tools, then open the Elements tab to see an example of what the class name looks like after compilation:

If you want to add more than one class, either use a package like classnames or just use native javascript template literals like so:

import styles from './button.module.css'
 
const UIButton: React.FC = (): JSX.Element => {
 
    return (
        <button className={`${styles.reset} ${styles.core}`}>
            I&apos;m a UI button
        </button>
    )
}
 
export default UIButton

Line 6: we use a javascript template literal to add two classes to the button (instead of just one)

Then we add the second class to our CSS Module:

.reset {
    background: none;
    border: none;
    padding: 0;
}
 
.core {
    --button-padding: 6px;
 
    padding: var(--button-padding);
    border: 2px dashed magenta;
}

If you want to use the element id instead of a class to style an element, you can do it like this:

<button id={styles.myIdStyle} className={`${styles.reset} ${styles.core}`}>

In the CSS module file, you add the corresponding CSS like this:

#myIdStyle {
    color: white;
    background-color: black;
    cursor:pointer;
}
 
 
#myIdStyle:hover {
    color: black;
    background-color: white;
}

Here are a few more things about CSS Modules worth knowing:

• CSS modules allow you to do composition by using the compose keyword, this works like an import in javascript and allows you to include one css module into another css module
• you can change the first part of the CSS Module filename (*.module.css) to whatever you want (I usually use the same name as the component), so if my component is Button.tsx, then my CSS module will be called button.module.css
• you can use CSS modules everywhere, they are not just for components, you can use them for pages and layouts, and you can place them anywhere, here we put them into the components folder, but you can also place them in the app folder if you prefer

Improved UI Button

The UI button we just created is an oversimplified version of a button component, in a real project, we would probably write something a little more useful like this:

'use client'
 
import type { PropsWithChildren } from 'react'
import type { Route } from 'next'
import styles from './button.module.css'
import { useRouter } from 'next/navigation'
 
interface IProps extends PropsWithChildren {
    url?: string
}
 
const UIButton: React.FC<IProps> = (props): JSX.Element => {
 
    const { url, children, ...rest } = props
    const router = useRouter()
 
    const clickHandler = () => {
        if (url) {
            router.push(url)
        }
    }
 
    return (
        <button onClick={clickHandler} id={styles.myIdStyle} className={`${styles.reset} ${styles.core}`} {...rest}>
            {children}
        </button>
    )
}
 
export default UIButton

Line 1: we use the 'use client' directive as we are going to add a click handler, if we don't explicitly mark it as a client component, Next.js will throw a runtime error like this one:

Error: Event handlers cannot be passed to Client Component props.
<button onClick={function clickHandler} className=... id=... children=...>
                ^^^^^^^^^^^^^^^^^^^^^^^
If you need interactivity, consider converting part of this to a Client Component.

Line 3: we import the PropsWithChildren type from react and line 4 we import the Route type from Next.js, so that lines 8 to 10 we can extend the default props type by adding an entry for our url prop, the url is of type Route and is followed by a question mark which indicates we want this to be an optional prop

Line 6: we import the Next.js useRouter hook, which will allow us to trigger a client-side navigation programmatically

Line 7: we import the Route type from Next.js

Line 12: because React.FC is a generic function it makes it easy for us to use our IProps interface, which will add type safety for the props

Line 14: we use the destructuring assignment to extract the variables we will use from the props object

Line 15: we create an app router instance

Lines 17 to 21: we create a click handler using an arrow function, it will check if the url prop is defined, if it is defined, we use the app router push method to perform a client-side navigation to the provided url

Line 24: we pass our event handler function to onClick

Line 25: we use the children prop to make our button component more flexible so that whoever uses the button can define what the button text should be instead of having a hardcoded text like before, of course, this makes it more reusable

Of course, now that we added a bit of reusability to our button, we also need to update the page in which we use the component to this:

import UIButton from '@/components/tutorial_examples/UI/Button'
 
export default function StylingExamplePage() {
 
    const goTo = '/'
 
    return (
        <>
            <UIButton url={goTo}>I&apos;m a UI button, that will open the homepage</UIButton>
        </>
    )
 
}

Line 9: the UIButton text is now defined between the opening and closing tag (and not hardcoded in the button itself anymore, making it more reusable), and we also pass it a url prop that we have set above in the page to activate the navigation feature

Adding a global.css

CSS Modules are perfect for styling components and even for styling the content in your pages, but at some point, you might want to add a class that can be used everywhere in your app, for example, have a global style for links, this is when you use the global.css

As we saw in the previous chapter, you can add classes and use the id in CSS Modules, but there is one thing you can't use in CSS Modules, and that's the Element type selectors

Let's (re-)open the CSS Module (that we created for our button) and add some styling for the button by using the button type selector, like so:

.reset {
    background: none;
    border: none;
    padding: 0;
}
 
.core {
    --button-padding: 6px;
 
    padding: var(--button-padding);
    border: 1px dashed orange;
}
 
button {
    color: blue;
}

Then make sure your dev server is running (using the npm run dev command), and you will see that you get an error in your terminal:

Syntax error: Selector "button" is not pure (pure selectors must contain at least one local class or id)

So instead, if you want to style all Elements that match a certain type, or if you want to add universal selectors (*), or set global css variables using the :root pseudo class, then you do it in the global.css, which we will create in the /app folder, with the following content:

:root {
    /* colors */
    --background-dark-value: 288 23% 20%;
    --background-dark-color: hsl(var(--background-dark-value));
    --text-dark-value: 19 71% 97%;
    --text-dark-color: hsl(var(--text-dark-value));
    --primary-dark-value: 315 60% 82%;
    --primary-dark-color: hsl(var(--primary-dark-value));
    --secondary-dark-value: 211 63% 83%;
    --secondary-dark-color: hsl(var(--secondary-dark-value));
    /* sizes */
    --spacing: 16px;
    --maxWidth: 1120px;
}
 
*,
*::after,
*::before {
    box-sizing: border-box;
}
 
html {
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    -webkit-text-size-adjust: 100%;
    text-size-adjust: 100%;
    tab-size: 4;
    background-color: var(--background-dark-color);
    color: var(--text-dark-color);
    font-size: 100%;
}
 
body {
    /* remove any margin that browsers add to body */
    margin: 0;
}
 
header {
    margin-bottom: var(--spacing);
}
 
footer {
    margin-top: var(--spacing);
    min-height: calc(var(--spacing) * 2);
}
 
main {
    display: flex;
    max-width: var(--maxWidth);
    margin-left: auto;
    margin-right: auto;
    margin-bottom: calc(var(--spacing) * 4);
}
 
/* on small screens */
@media all and (max-width: 768px) {
    main {
        margin-bottom: calc(var(--spacing) * 2);
        /* place one under the other */
        flex-flow: column;
    }
}
 
article,
section {
    padding: var(--spacing);
    width: 100%;
}
 
p {
    margin-block: 1em;
}
 
a {
    color: var(--primary-dark-color);
}
 
a:hover {
    color: var(--secondary-dark-color);
}
 
h1 {
    font-size: 6rem;
    line-height: 1.167;
}
 
h2 {
    font-size: 3.75rem;
    line-height: 1.2;
}
 
h3 {
    font-size: 3rem;
    line-height: 1.167;
}
 
h4 {
    font-size: 2.125rem;
    line-height: 1.235;
}
 
h5 {
    font-size: 1.5rem;
    line-height: 1.334;
}
 
h6 {
    font-size: 1.25rem;
    line-height: 1.6;
}
 
h1 {
    margin-block: 0 1em;
}
 
h2,
h3,
h4,
h5,
h6 {
    margin-block: 1.5em 1em;
}

This is our base global.css which now contains a basic CSS (Cascading Style Sheet) used to style and layout our app:

Lines 1 to 14: we set some variables (inside of the :root pseudo class) that can be used everywhere (even in any of our CSS Modules), it is recommended to use CSS variables whenever possible as in the future it will be faster to change the value of a variable in the global css instead of having to go into every file where that variable gets used and change the value there

Line 16 to 20 we use a technique seen in a lot of reset stylesheets, we use an asterisk (*) to target all elements of our HTML document and then also include their ::before and ::after pseudo elements, we set their box-sizing CSS property to border-box; this will impact how the browser calculates the width and height of elements, by default box-sizing is set to content-box, in which case the width and height only include the content but NOT the border (width), padding or margin; we change box-sizing to border-box, so now the width and height will also include the border and padding but still not the margin; this way of calculating the width and height seems more intuitive then the default behavior to a lot of developers, which is why this is something you will often see in stylesheets (if however you prefer the default behavior, then feel free to not include this part in your own global.css stylesheet)

Lines 22 to 31: we use the html type selector and do several things:

• first, set the font-smoothing CSS property to tell the browser to apply anti-aliasing to our fonts, if you have a dark background and light text (which we do in this example) then anti-aliasing can prevent the text from looking overly bold and instead makes it look lighter, but be aware that on the caniuse CSS font-smooth page they say that this property is not part of the CSS standard, however, both webkit and firefox implement their own nonstandard property; as explained in the article "stop-fixing-font-smoothing" this feature should only get used for light fonts on dark backgrounds but not for dark text on a light background, I recommend reading that article if you want to learn more about font smoothing
• then we also set the text-size-adjust CSS property, this feature makes sure that on mobile browsers, the text size is exactly the one we set and not inflated by the browser, this helps to avoid weird placement bugs where modified text size moves other elements around; however, if you use this feature make sure that your text is easy to read on mobile devices and tablets, if the text is too small I recommend using a bigger font-size and always keep the text-size-adjust set to 100%, text-size-adjust is however only supported on chrome (as of now); you can check out what browser support it on caniuse "text-size-adjust"
• we also use the tab-size CSS property, which is useful if, for example, you have code blocks in your content, as code blocks often contain tabs for code indentation, which means this feature is similar to setting the indent size in your .editorconfig file, if you use just a number without a unit (like in this example) then tab size will be that number multiplied by the width of one space (this is MOT the font-size, which is the height of your characters); so setting it to 4 and assuming a space character is 9px wide then this gives us a tab size width of 4 x 9 = 36px
• then we set the color for our background and the default color for our text using the CSS var() function and as value we use the colors we previously defined in the :root pseudo element
• finally, we set the font-size to 100%, which is good for accessibility as it lets the user change the font-size via the browser settings; as we will also use the CSS rem unit for all font related sizes, this means that setting the font-size of the HTML element will have an impact on all other font-sizes in our CSS; for example, we use the CSS rem unit for the font-size of all our headings, if the user now changes the default font-size via the browser settings then all our text will adapt to that change but also all the headings will get adjusted based on the new default font-size; however, if you would have set a static value like 16px as font-size to your <html> element (or the <body> element) then the user would NOT be able to change the font-size via the browser settings, as their settings would have no effect, the font would still be 16px

Lines 33 to 36: we use the body type selector and reset the margin value(s) that a browser might set by default, to zero

Lines 38 to 45: we add some margin to the footer and header using the respective type selectors, we also add a minimum height to the footer, which will create a bit of space at the end of our pages, this is useful as on mobile and tablet you sometimes have a device or browser UI that will put something on the bottom of the screen that would be over your last bit of content, making the bottom part hard to read or even prevent interacting with something in your page. By adding a bit of space you ensure that the user will always see all of your content (when the page is fully scrolled down)

Lines 47 to 53: we use the main type selector to tell the browser that we want to use the CSS Flexbox layout by setting the display property to flex; for this element we set a maximum width using the CSS variable we created in the :root, the maximum width is 1120px to ensure that even on very large viewports (screens) the main element will not stretch to the full available width, this is important for the text we will place inside of our main section because if chapters of the text are very wide, it makes them hard to read; we set both the margin-left and margin-left to auto to make sure that our <main> element will get centered if the viewport is wider than the max-width we just set; finally, we also add a little bit of margin to the bottom to make sure there is a bit of space between our content and the footer of the page

Lines 55 to 62: here we change the flex-flow of the <main> element to column, which means that this time if we put an <article> into our <main> as well as an <aside> then both will get displayed as two rows, we do this because on devices with a viewport smaller than the maximum width of 768px, which we are targetting with our @media all and (max-width: 768px) media query, we want the <aside> element to get placed below the <article>

Lines 64 to 68: we add padding to sections and articles on each side using our --spacing CSS variable (16 pixels); as we also added maximum width to the main element, this means that the article content (if we don't have an <aside> element) will be a maximum 1120 - (2*16) = 1088 pixels wide; this will matter in a future chapter when we start adding images to our content; finally we set the width to 100% to make sure that the <article> element always uses the full width of the parent <main> element

Lines 70 to 72: we use the margin-block CSS property (which is a shorthand for margin-block-start and margin-block-end) and define the size using em units, which will result in a margin on the top and bottom of every paragraph; the size of the margin will be relative to the font-size used by the paragraph as the unit we use is em (1em when used for the margin is 1 time the elements font-size); be aware that caniuse states that margin-block is supported by all modern browsers but NOT supported by IE11

Lines 74 to 80: we add some color to all our links using the CSS var() function to use the variables we set earlier in the root, and we also use the :hover pseudo class to change the color of links on hover

Lines 82 to 110: we use the font-size and line-height properties to set a custom height for our headings (like any other values in this CSS stylesheet, those are just my examples, feel free to tweak those values to your liking)

Lines 112 to 122: we set the margin for the headings, same as for the paragraph(s) we use the margin-block CSS property and em units, meaning the margins will be relative to the headings font-size (the bigger the font-size of the heading the bigger the margin will be)

Adding the global.css to the layout

Now, to apply the global styles to our content, we are going to import the global.css inside of our root layout (located in the /app folder) like so:

import './global.css'
import { Metadata } from 'next'
 
export const metadata: Metadata = {
    title: 'Next.js',
    description: 'Generated by Next.js',
}
 
export default function RootLayout({
    children,
}: {
    children: React.ReactNode
}) {
    return (
        <html lang="en">
            <body>
                <header>
                    <p>My Header</p>
                </header>
                <main>{children}</main>
                <footer>
                    <p>My Footer</p>
                </footer>
            </body>
        </html>
    )
}

Line 1: we import our global.css stylesheet, and that's already it

Line 2: we re-add the Metadata type import, that got stripped from the layout when Next.js created a new one (as we had deleted ours), but it forget to add the type that create next app would add

Line 17 to 23: we add some new semantic elements, like a <header>, a <main> and a <footer> element, now that we added some CSS for them in our global.css file

Now (make sure your dev server is running) visit the previous example page we did in your browser http://localhost:3000/styling, you will already see how the background color of our page has changed and see that we now have new elements like the header and footer of our layout, that get rendered on top and bottom of our main element

Congratulations 🎉 you now know how to use CSS modules and global.css to add styling to your project

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