LESS WEB DEVELOPMENT ESSENTIALS: Use CSS preprocessing to streamline the development and maintenance of your web applications

In web design, you will use HTML to describe the structure of your documents and CSS language to describe their presentation, including fonts, colors, and layout. The current standard HTML5 and CSS3 versions work on most modern browsers and mobile devices. CSS3 extends the old CSS with other new selectors, text effects, background gradients, and animations. The power of CSS3, the new functionalities, and high acceptance on mobile devices using HTML5 and CSS3 make them the standard for modern web design. The combination of HTML5 and CSS3 is ideal for building responsive websites because of their high acceptance on mobile phones (and other devices).

Together, HTML5 and CSS3 introduce many new features. You will be shown the ones that are the most significant when learning about their concepts within this book.

Specificity, Inheritance, and Cascade in CSS

In most cases, many CSS styles can be applied on the same HTML element, but only one of them will win. W3C specifications describe the rules for which CSS styles get the most precedence and will ultimately be applied. You can find these specifications in the following section.

The rules regarding the order of importance have not significantly changed with CSS3. They are briefly mentioned to help you understand some of the common pitfalls with Less/CSS and how to solve them. Sooner or later, you will be in a situation where you're trying to apply a CSS style to an element, but its effect stays invisible. You will reload, pull out your hair, and check for typos again and again, but nothing will help. This is because in most of these cases, your style will be overruled with another style that has a higher precedence.

The global rules for Cascade in CSS are as follows:

• Find all the CSS declarations that apply to the element and property in question.

• Inline styles have the highest precedence, except for !important. The !important statement in CSS is a keyword used to add weight to a declaration. The !important statement is added at the end of a CSS property value. After this, check who set the declaration; styles set by the author get a higher precedence than the styles defined by the user or browser (default). Default means the styles are set by the web browser, author styles are defined by CSS in the web page, and user styles are set by the user via the settings of his or her web browser. The importance of the user is higher than the default, and the code with the !important statement (see Chapter 2, Using Variables and Mixins for its meaning in Less) will always get the highest precedence. Note that browsers such as Firefox have options to disable pages in order to use other alternatives to user-defined fonts. Here, the user settings overrule the CSS of the web page. This way of overruling the page settings is not part of the CSS precedence unless they are set using !important.

• Calculate the specificity, which is discussed in the following section.

• If two or more rules have the same precedence and specificity, the one declared last wins.

As a Less/CSS designer, you will be making use of the calculated CSS specificity in most cases.

How CSS specificity works

Every CSS declaration gets a specificity, which will be calculated from the type of declaration and the selectors used in its declaration. Inline styles will always get the highest specificity and will always be applied (unless overwritten by the first two Cascade rules). In practice, you should not use inline styles in many cases as it will break the DRY principle. It will also disable you from changing your styles on a centralized location only and will prevent you from using Less for styling.

An example of an inline style declaration is shown as follows:

<p style="color:#0000ff;">

After this, the number of IDs in the selector will be the next indicator to calculate specificity. The #footer #leftcolumn {} selector has 2 IDs, the #footer {} selector has 1 ID, and so on.

Tip

Note that in this case, an ID is a unique selector starting with #; the selector [id=] for the same HTML element counts as an attribute. This means that div.#unique {} has 1 ID and div[id="unique"] {} has 0 IDs and 1 attribute.

If the number of IDs for two declarations is equal, the number of classes, pseudo classes, and attributes of the selector will be of importance. Classes start with a dot. For example, .row is a class. Pseudo classes, such as :hover and :after, start with a colon, and attributes, of course, are href, alt, id, and so on.

The #footer a.alert:hover {} selector scores 2 (1 class and 1 pseudo class) and the #footer div.right a.alert:hover {} selector scores 3 (2 classes and 1 pseudo class).

If this value is equal for both declarations, we can start counting the elements and pseudo elements. The latest variable will be defined with a double colon (::) . Pseudo elements allow authors to refer to otherwise inaccessible information, such as ::first-letter. The following example shows you how that works.

The #footer div a{} selector scores 2 (2 elements) and the #footer div p a {} selector scores 3 (3 elements).

You should now know what to do when your style isn't directly applied. In most cases, make your selector more specific to get your style applied. For instance, if #header p{} doesn't work, then you can try adding a #header #subheader p{} ID, a #header p.head{} class, and so on.

When Cascade and !important rules do not give a conclusive answer, specificity calculation seems to be a hard and time-consuming job. Although Less won't help you here, tools such as Firebug (and other developer tools) can make the specificity visible. An example using Firebug is shown in the following screenshot, where the selector with the highest specificity is displayed at the top of the screen and the overruled styles are struck out:

An example of specificity in Firebug

div#wrapper {
  display: -webkit-flex;
  display: -moz-flex;
  display: -ms-flexbox;
  display: -ms-flex;
  display: flex;
}

div#wrapper { .flex-display; }

After delving into the theory of CSS, you can finally start using Less. As mentioned earlier, it has the same syntax as CSS. This means any CSS code is, in fact, a valid Less code too. With Less, you can produce CSS code that can be used to style your website. The process used to make CSS from Less is called compiling, where you can compile Less code via the server side or client side. The examples given in this book will make use of client-side compiling. Client side, in this context, means loading the code in a browser and compiling Less code into CSS code using resources from the local machine. Client-side compiling is used in this book because it is the easiest way to get started while being good enough for developing your Less skills.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">

  <title>Example code</title>
  <meta name="description" content="Example code">
  <meta name="author" content="Bass Jobsen">

  <link rel="stylesheet/less" type="text/css" href="less/styles.less" />
   <script src="less.js" type="text/javascript"></script>
</head>

<body>
<h1>Less makes me Happy!</h1>
</body>
</html>

<link rel="stylesheet/less" type="text/css" href="less/styles.less" />

<script src="less.js" type="text/javascript"></script>

h1{color:red;}

Debugging your code

As we are only human, we are prone to making a mistake or a typo. It is important to be able to see what you did wrong and debug your code. If your Less file contains errors, it won't compile at all. So, one small typo breaks the complete style of the document.

Debugging is also easy with less.js. To use debugging or allow less.js to display errors, you can add the following line of code to your index.html:

  <link rel="stylesheet/less" type="text/css" href="less/styles.less" />
  <script type="text/javascript">less = { env: 'development' };</script>
  <script src="less.js" type="text/javascript"></script>

As you can see, the line with less = { env: 'development' }; is new here. This line contains less as a JavaScript variable used by less.js. In fact, this is a global Less object used to parse some settings to less.js. The only setting that will be used in this book is env: 'development'. For more settings, check out the following website: http://lesscss.org/#client-side-usage-browser-options.

Tip

env: 'development' also prevents Less from caching. Less doesn't cache files in the browser cache. Instead, files are cached in the browser's local storage. If env is set to production, this caching could yield unexpected results as the changed and saved files are not compiled.

To try this new setting, edit less/styles.less again and remove an accolade to create an invalid syntax of the h1{color:red form and then save the file.

In your browser, you will see a page like the following screenshot:

An example of a Less parse error

Besides syntax errors, there will also be name errors that are displayed. In the case of a name error, an undeclared function or variable would have been used.

It is possible to set other settings for debugging, either in the global Less object or by appending the setting to the URL. For example, you can specify the dumpLineNumbers setting by adding the following lines of code to your HTML file:

<script type="text/javascript">less = { env: 'development',dumpLineNumbers: "mediaQuery"
 };</script>

Alternatively, you can add !dumpLineNumbers:mediaQuery to the URL. This setting enables other tools to find the line number of the error in the Less source file. Setting this option to mediaQuery makes error reporting available for the FireBug or Chrome development tools. Similarly, setting this to comments achieves the same for tools such as FireLess. For instance, using FireLess allows Firebug to display the original Less filename and the line number of CSS styles generated by Less .

FireBug, Chrome development tools, or the default browser inspect the element functions (which you can access by right-clicking on your browser screen) can also be used to see and evaluate the compiled CSS. The CSS is displayed as inline CSS wrapped inside a <style type="text/css" id="less:book-less-styles"> tag. In the example given in the following screenshot, you will see an ID with value less:book-less-styles. The value of this ID have been automatically generated by Less based on the path and name of the book/less/styles.less Less file:

Less-generated CSS styles

Example code used in this book

In this book, you will find many code examples. Unless explicitly mentioned, the format of these examples always shows the Less code first, followed by the compiled CSS code. For instance, you can write the following lines of code in Less:

mixin() {
color: green;
}
p {
.mixin();
}

This code will be compiled into the following CSS syntax :

p {
color: green;
}

You must first open first.html (from the downloadable files for the book) in your browser and then open less/first.less in your text editor. In your browser, you will see a representation of a header, body, and footer.

As expected, less/first.less contains the Less code that will be converted into valid CSS by the less.js compiler. Any error in this file will stop the compiler and throw an error. Although the Less code shows some similarities to the plain CSS code, the process described here totally differs from editing your CSS directly.

The following screenshot shows you how this layout will look when opened in your web browser:

Your first layout in Less

-webkit-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px;

#header{
background-color: red;
-webkit-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px;
}

#header, #content, #footer{
-webkit-border-radius: 10px;
-moz-border-radius: 10;
border-radius: 10px;
}

.roundedcornersmixin()
{
-webkit-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px;
}

#header{
background-color: red;
.roundedcornersmixin();
}

#header{
background-color: red;
-webkit-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px;
}

.roundedcornersmixin(@radius: 10px){
-webkit-border-radius: @radius;
-moz-border-radius: @radius;
border-radius: @radius;
}

/* mixins */
.roundedcornersmixin(@radius: 10px){
-webkit-border-radius: @radius;
-moz-border-radius: @radius;
border-radius: @radius;
}
#header{
background-color: red;
.roundedcornersmixin();
}
#content{
background-color: white;
min-height: 300px;
.roundedcornersmixin(20px);
}
#footer{
background-color: navy;
.roundedcornersmixin();
}

When talking about cascade in CSS, there will no doubt be a mention of the browser default settings getting a higher precedence than the author's preferred styling. When writing Less code, you will overwrite the browser's default styling. In other words, anything that you do not define will be assigned a default styling, which is defined by the browser. This behavior plays a major role in many cross-browser issues. To prevent these sorts of problems, you can perform a CSS reset. The most famous browser reset is Eric Meyer's CSS Reset (accessible at http://meyerweb.com/eric/tools/css/reset/).

CSS resets overwrite the default styling rules of the browser and create a starting point for styling. This starting point looks and acts the same on all (or most) browsers. In this book, normalize.css v2 is used. Normalize.css is a modern, HTML5-ready alternative to CSS resets and can be downloaded from http://necolas.github.io/normalize.css/. It lets browsers render all elements more consistently and makes them adhere to modern standards.

To use a CSS reset, you can make use of the @import directive of Less. With @import, you can include other Less files in your main Less file. The syntax is @import "{filename}";. By default, the search path for the directives starts at the directory of the main file. Although setting alternative search paths is possible (by setting the path's variable of your Less environment), it will not be used in this book.

The example Less files in this book will contain @import "normalize.less"; in the first few lines of the code. Again, you should note that normalize.less does contain the CSS code. You should pay particular attention to the profits of this solution!

If you want to change or update the CSS reset, you will only have to replace one file. If you have to manage or build more than one project, which most of you should be doing, then you can simply reuse the complete reset code.

Creating background gradients

A new feature in CSS3 is the possibility of adding a gradient in the background color of an element. This acts as a replacement for complex code and image fallbacks.

It is possible to define different types of gradient and use two or more colors. In the following figure, you will see a background gradient of different colors:

A gradient example (from W3schools.com)

In the next example, you can use a linear gradient of two colors. The background gradients use vendor-specific rules.

You can make use of the example code from the rounded corners example to add gradients to it.

The first step is to copy or open less/gradient.less and add a new mixin at the start of this file as shown in the following code:

/* Mixin */
.gradient (@start: black, @stop: white,@origin: left) {
    background-color: @start;
    background-image: -webkit-linear-gradient(@origin, @start, @stop);
     background-image: -moz-linear-gradient(@origin, @start, @stop);
    background-image: -o-linear-gradient(@origin, @start, @stop);
    background-image: -ms-linear-gradient(@origin, @start, @stop);
    background-image: linear-gradient(@origin, @start, @stop);
}

This will create gradients from the left (@origin) to the right with colors from @start to @stop. This mixin has default values.

IE9 (and its earlier versions) do not support gradients. A fallback can be added by adding background-color: @start;, which will create a uniform colored background for older browsers.

After adding the mixin to your code, you can call on it for our #header, #body, and #footer selectors as shown in the following code:

#header{
background-color: red;
.roundedcornersmixin();
.gradient(red,lightred);
}
#content{
background-color: white;
min-height: 300px;
.roundedcornersmixin(20px);
.gradient();
}
#footer{
background-color: navy;
.roundedcornersmixin(20px);
.gradient(navy,lightblue);
}

For example, if you renamed the Less file to less/gradient.less, you would have also had to change the reference in your HTML file to the following code:

<link rel="stylesheet/less" type="text/css" href="less/gradient.less" />

If you now load the HTML file in the browser, your results should be like the following screenshot:

Gradients in the header, content, and footer from the example code

Another new feature in CSS3 is the presence of transitions, transformations, and animations. These functions can replace the animated images, flash animations, and JavaScripts in the existing or new web pages. The difference between transitions, transforms, and animations isn't trivial. Animations are constructed with a range of @keyframes, where each @keyframes handles different states of your element in time. Transitions also describe the state of element between start and end. Transitions are mostly triggered by CSS changes, such as a mouse over (hover) of an element.

To make things clear, it is important to keep in mind the button that is about to be pressed. The button will have two states: pressed and not pressed. Without transitions and animations, we are enabled to style these states only. The color of the button is white, and its color becomes red when you hover the mouse over it. (In CSS terms, its state becomes hovered by adding the :hover pseudo class.) In this case, the transition describes how the hovered button becomes red. For example, the change in color from white to red in two seconds (which makes it pink halfway) shows that the start of the color change is slow and changes faster as time passes. Using animations here enables us to describe the state of the button for every time interval between the start and end. For example, you don't have to change the color from white to red, but the change covers all the states, from white, blue, green, and finally to red.

Transformations change the position of an element and how it looks. They do not depend on the state of the element. Some of the possible transformations are scaling, translating (moving), and rotating.

In practice, we use a combination of animations, transformations, and/or transitions in most situations. Also, in this case, vendor-specific rules will play an important role.

Now, a transformation will be added to our example.

Using the example code with rounded corners and gradients, copy the following code to less/transition.less or open less/transition.less and add the following code to the beginning of the file:

/* Mixin */
.transition (@prop: all, @time: 1s, @ease: linear) {
-webkit-transition: @prop @time @ease;
-moz-transition: @prop @time @ease;
-o-transition: @prop @time @ease;
-ms-transition: @prop @time @ease;
transition: @prop @time @ease;
}

This mixin has three variables; the first will be the property (@prop) that you will change. This can be height, background-color, visibility, and so on. The default value all shouldn't be used in the production code as this will have a negative effect on performance. @time sets the duration in milliseconds or seconds with s appended to it. The last variable, @ease, sets the transition-timing-function property. This function describes the value of a property, given that a certain percentage of it has been completed. The transition-timing-function property describes the completeness of the transition as a function of time. Setting it to linear shows the effect with the same speed from start to end, while ease starts slow and ends slow, having a higher speed in the middle. The predefined functions are ease, linear, ease-in, ease-out, ease-in-out, step-start, and step-end.

Now, you can edit less/transition.less to use this mixin. You can set the background color of the body when you hover over it. Note that you don't need to use the transition to change the gradient color but rather change the background-color attribute. You are using background-color because transition-duration doesn't have a visible effect on the gradient. The code of the background-color transition is as follows:

#content{
background-color: white;
min-height: 300px;
.roundedcornersmixin(20px);
.transition(background-color,5s);
}
#content:hover{
background-color: red;
}

If you renamed the Less file, for example, to less/transition.less, you would also have to change the reference in your HTML file to the following code:

 <link rel="stylesheet/less" type="text/css" href="less/transition.less" />

If you load the HTML file in the browser, you will be able to see the results in the browser. Move your mouse over the content and see it change from white to red in 5 seconds.

Finally, a second example that rotates the header can be added. In this example, you will use @keyframes. Using @keyframes will be complex. So, in this case, you can define some vendor-specific rules and add these animation properties to #header: as follows:

@-moz-keyframes spin { 100% { -moz-transform: rotate(360deg); } }
@-webkit-keyframes spin { 100% { -webkit-transform: rotate(360deg); } }
@keyframes spin { 100% { -webkit-transform: rotate(360deg); transform:rotate(360deg); } }
#header{
    -webkit-animation:spin 4s linear infinite;
    -moz-animation:spin 4s linear infinite;
    animation:spin 4s linear infinite;
}

You can add the preceding code to our example files or open less/keyframes.less.

If you renamed the Less file, for example, to less/keyframes.less, you also have to change the reference in your HTML file to the following code:

 <link rel="stylesheet/less" type="text/css" href="less/keyframes.less" />

Now, load the HTML file in the browser and watch your results. Amazing, isn't it? With a little bit of creative thinking, you will see the possibilities of creating a rotating windmill or a winking owl using only CSS3. However, the first thing that should be done is to explain the code used here in more detail. As mentioned earlier, there are many cases in which you would make combinations of animations and transformations. In this example, you also get to animate a transformation effect. To understand what is going on, the code can be split into three parts.

The first part is @keyframes, shown in the following code, which describe the value of the CSS properties (transformation in this case) as a function of the percentage of the animation completeness:

@keyframes spin { 100% { -webkit-transform: rotate(360deg); transform:rotate(360deg); } }

These keyframes have been given the name reference spin, which is not a special effect but only a chosen name. In the preceding example, a state of 100 percent completeness is described. At this state, the animated element should have made a rotation of 360 degrees.

This rotation is the second part that needs our attention. The transformation describes the position or dimensions of an element in the space. In this example, the position is described by the number of degrees of rotation around the axis, 360 degrees at 100 percent, 180 degrees at 50 percent, 90 degrees at 25 percent, and so on.

The third part is the animation itself, described by: animation:spin 4s linear infinite;. This is the shorthand notation of settings of the subproperties of the animation property. In fact, you can write this as the following code, without the vendor-specific rules:

animation-name: spin;
animation-duration: 4s;
animation-timing-function:linear;
animation-iteration-count:  infinite;

You can use these three parts to build a complete animation. After doing this, you can extend it. For example, add an extra keyframe, which makes the time curve nonlinear, as follows:

@keyframes spin {
50% { transform: rotate(10deg);}
100% {transform: rotate(360deg); }
 }

You can add a second property using background-color. Don't forget to remove the gradient to see its effect. This is shown in the following code:

@-moz-keyframes spin {
50% { transform: rotate(10deg); background-color:green;}
100% { transform: rotate(360deg); }
 }
//.gradient(red,yellow);

You will have noticed that the complete profit of using Less isn't realized here. You will have to write the @keyframes definition repeatedly due to its variable animation name. In Chapter 4, Avoid Reinventing the Wheel, a solution will be provided to you for this.

Unfortunately, browser support for transitions, transformations, and animations is not great and varies between browsers. Google Chrome does not support CSS 3D transforms, Firefox lacks support for CSS Filters, and IE9 (and earlier versions) don't support them at all. To solve this, many developers look to jQuery to support their animations. The jQuery.animate() function allows us to change the CSS properties of the elements using JavaScript. You can still use Less to set the initial CSS. An alternative for this will be to use animate.css (which you can access at https://github.com/daneden/animate.css); this cross-browser library of CSS animations gets converted into Less code with a jQuery fallback.

The box-sizing property is the one that sets the CSS-box model used for calculating the dimensions of an element. In fact, box-sizing is not new in CSS, but nonetheless, switching your code to box-sizing: border-box will make your work a lot easier. When using the border-box settings, calculation of the width of an element includes border width and padding. So, changing the border of padding won't break your layouts. You can find a copy of the code used in this section in boxsizing.html from the download files.

Nowadays, most web designs use a grid. Grids split your design into columns of equal size. This helps you make things clear and build responsive interfaces. Depending on the available screen size (or width), you can show your content and navigation with a different representation of the same columns.

To handle different screen sizes, some parts of your website will have fluid width or height. Other elements, such as borders, gutters, and the white space, should have a fixed width. The combination of fluid widths as a percentage of the screen width (or viewport) with fixed widths becomes complex. This complexity will be due to the fact that browsers use different calculations for padding and margins of elements.

In order for you to see this, look at the following example. A container of 500 pixels width has been created. Inside this container, you can add two rows and split the second row into two parts of 50 percent (or half) width.

<div class="wrapper" style="width:300px;">
  <div style="background-color:red;width;100%;">1</div>
  <div style="background-color:green;width:50%;float:left;">2</div>
  <div style="background-color:blue;width:50%;float:right;">3</div>
</div>

This will now look like the following screenshot:

An HTML wrapper

The current structure doesn't show a problem until you add some padding, which is used to construct some space or a border between the two columns on the second row (numbers 2 and 3 in the image of the HTML wrapper). The padding and the border will break our layout as follows:

<div class="wrapper" style="width:300px;">
<div style="background-color:red;width:100%;">1</div>
<div style="background-color:green;width:50%;float:left;border:5px solid yellow;">2</div>
<div style="background-color:blue;width:50%;border:5px solid yellow;float:right;">3</div>
</div>
<br>
<div class="wrapper" style="width:300px;">
<div style="background-color:red;width;100%;">1</div>
<div style="background-color:green;float:left;width:50%;padding-right:5px;"><div style="background-color:yellow;">2</div></div>
<div style="background-color:blue;width:50%;padding-right:5px;float:right;">3</div>
</div>

Finally, the output of this code should look like the following screenshot:

A broken layout due to padding and borders

A similar action can be performed, except that the wrappers can be wrapped inside an extra wrapper. The box-sizing: border-box; declaration can then be applied to this. Now, the results should look like the following screenshot:

A layout with box-sizing: border-box

As you can see, the padding and borders are subtracted by 50 percent from the parent. This will make the calculation a lot easier. Of course, you can do the calculating yourself once the parent container wrapper has a fixed width. If the parent has 300 pixels, then 50 percent of this will be 150 pixels. Taking away the padding and the width of the border will give you the fixed size of a column. This won't work when your parent has a fluid width (the percentage of the viewport). Fluid layouts change their width with the width of the screen. If your screen becomes smaller, then all the elements become smaller too and the percentage stays equal. By doing calculations for all the possible screen sizes to find the real size of a column that allows all of your elements to align, you will quickly find this to be a long, challenging, and arduous process.

For these reasons, you should make use of box-sizing: border-box; for all the examples in this book. Please note that box-sizing has to also be defined by vendor-specific rules as follows:

-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;

In this example, the Less code will be as follows:

// Box sizing mixin
.box-sizing(@boxmodel) {
  -webkit-box-sizing: @boxmodel;
     -moz-box-sizing: @boxmodel;
          box-sizing: @boxmodel;
}
// Reset the box-sizing
*,
*:before,
*:after {
  .box-sizing(border-box);
}

@import: "normalize.less";
@import: "boxsizing.less";

In the following chapters, you will learn more about organizing your Less code into files.

You have taken the first few steps towards Less development already. As explained earlier, client-side compiling has been used. However, client-side compiling with less.js shouldn't be used on real websites. This is because despite making your development easy and fast, compiling your Less files for every page request (or in fact, initial page load per user) will actually slow down your website.

For the production environment, it is required that you compile your files and serve the final CSS file to the browser. The term server side can be somewhat misleading. Server side in this context means a compiled CSS code is sent to the client's browser instead of Less code, which has to be compiled in the client's browser by less.js before it is shown. You should precompile your Less code. By copying and pasting the results of less.js to a file and including this as a CSS file in your HTML files, you should have the same effect, except that your CSS is not minimized.

Less bundles a command-line compiler. Installing and using it is simple using the following command:

 >> npm install -g less
 >> lessc styles.less styles.css

The package manager for the Node JavaScript platform is npm. Node enables you to run Java scripts without a browser. Node and npm run on Windows, Mac OS X, and other Unix/*nix machines. You will find the Node.js source code or a prebuilt installer for your platform by visiting http://nodejs.org/download/. To install npm, please read the instructions in the README file by visiting https://www.npmjs.org/doc/README.html.

Use the –help function to get a list of options you can use with the following command-line compiler:

 >> lessc –help

lessc styles.less styles.css compiles styles.less to styles.css. The links to styles.css in your HTML after successfully compiling it are then shown as follows:

<link rel="stylesheet/css" type="text/css" href="styles.css">

In this chapter, you refreshed and extended your knowledge about CSS3. You learned how to compile your Less code on the client side. Furthermore, you have written the code that allows you to have rounded corners, gradients, and animations in Less, so you can now witness the profits of using Less and take the crucial initial steps to organize and plan your new projects. You witnessed why you would want to use CSS resets, how to compile these into Less code, as well as how the box-sizing border-box can make your job easier. You also saw what a mixin is, how to use it, and how you can import a Less file with the @import directive. Last but not least, you have learned what server-side compiling is and how to use GUIs.

In the next chapter, you will learn how to use variables in Less and how to build and use complex mixins.