What are cascading style sheets(CSS)?

History and evolution of CSS

The beginnings of CSS

CSS was introduced in 1996 by the W3C (World Wide Web Consortium) organization as a solution to the problem of separating a document’s structure from its visual style. Previously, all styles were defined directly in HTML, leading to pages that were difficult to manage and inflexible. The first version of CSS, called CSS1, was simple and included basic features such as text formatting, margins, colors and alignment.

CSS standards development

After the introduction of CSS1, the technology evolved rapidly, introducing new features and expanding the possibilities of web styling:

1. CSS2 (1998):
   • Included improvements to layouts, such as support for absolute and relative positions, defining layers (z-index) and support for print media.
   • Introduced support for pseudo-elements and pseudo-classes, which allowed for more advanced style manipulation.
2. CSS3 (2011):
   • The biggest breakthrough in the history of CSS. The specification was divided into modules, which allowed independent development of various features.
   • It introduced many modern features such as:
     • Animations and transitions.
     • Flexbox and Grid Layout for advanced layout management.
     • Support for variables, gradients, shadows and rounding.
     • Media queries that enabled responsive page design.
3. CSS4 (currently in development):
   • CSS4 is not a one-time release, but a continuation of the modular development of CSS3.
   • It introduces advanced features such as Container Queries, which allow styles to be customized based on the size of the container rather than the entire view.
   • Improvements in selector specificity, such as new pseudo-classes (:is(), :where()).

The importance of the CSS language for the development of the Internet

Cascading style sheets have played a key role in the evolution of the Internet, enabling the design of more aesthetically pleasing and useful websites. They have made it possible to create sites that are:

• Aesthetically advanced: Complex visual effects and animations have improved the quality of designs.
• Responsive: Media queries have made it possible to adapt pages to different devices, which is the standard today.
• Accessible: CSS supports accessibility of pages, enabling design for people with different needs.

Why use CSS?

The main purpose of CSS is to simplify the web design process by separating the structure (HTML) from the visual layer. There are many benefits to using CSS:

1. Simplified style management: Instead of defining styles for each element separately in the HTML code, you can define common rules in one place. This way, changing the appearance of an entire page requires editing only one CSS file.
2. Visual consistency: CSS allows the same styles to be used on different pages within a single site, providing a consistent look and user experience.
3. Less HTML code: Moving style rules to external CSS files makes the HTML code cleaner and clearer, improving readability.
4. Easier adaptation to different devices: CSS allows you to create responsive designs that automatically adapt to screens of different resolutions, from phones to computer monitors.

Basic principles of CSS

The structure of CSS is based on rules, which consist of selectors, indicating HTML elements, and declarations containing properties and their values, which define the appearance of these elements. Thus, CSS allows precise control over the styling of web pages.

CSS works by defining styles in the form of rules consisting of:

• Selectors: Specify which HTML elements are to be styled (e.g. h1, .class, #id).
• Declarations: Contain properties and their values that define the appearance of elements. Example:

h1 {
    color: blue;
    font-size: 24px;
}

Each rule consists of a selector, and the properties and values are specified in curly brackets.

Cascading

CSS works in a “cascading” way, which means that styles are applied according to a certain priority:

1. Inline styles: styles written directly into the HTML element using the style attribute , e.g. <p style="color: red;">.
2. Internal (embedded) styles: defined in the <style> section in the header of the HTML document.
3. External styles: defined in a separate .css file and attached to the HTML document using <link>.

If the styles conflict, the higher-priority rules overwrite the lower-priority ones.

Specificity and validity

Each CSS rule has a specific weight based on the selector:

• Least specificity: Element selectors (e.g., p).
• Medium specificity: Class selectors (e.g. .class).
• Highest specificity: ID selectors (e.g. #id).
• Rules marked as !important have the highest priority and override other styles, regardless of specificity.

Inheritance

Some CSS properties are automatically inherited by descendant elements, such as:

• Inheritance: color, font-family.
• Non-inherited: margin, padding, border (you need to define them manually if you need them).

Inheritance values can be enforced using inherit:

p {
    color: inherit;
}

CSS types and sources

CSS can be used in three different ways, depending on the needs of the project and the scope of the application:

1. Style inline

• Styles defined directly in the style attribute of the HTML element. Example:

<p style="color: blue; font-size: 16px;">Text</p>

Pros: Fast and easy to use in simple projects.

Cons: Difficult to manage in large projects, does not support cascading and inheritance.

Internal styles (embedded CSS)

• Styles placed in the <style> section in the header of an HTML document. Example:

<style>
    p {
        color: green;
        font-size: 18px;
    }
</style>

Pros: Useful when styling a single page.

Cons: Limited flexibility for larger projects.

External styles

• Styles defined in a separate .css file that is appended to the HTML using <link>. Example:

<link rel="stylesheet" href="styles.css">

Advantages:

• Best solution for large projects.
• Allows you to reuse the same styles on multiple pages.
• Makes code easier to manage and maintain.

Disadvantages:

• Requires loading an additional file, which can minimally increase page load time.

Practical application of CSS

CSS allows you to precisely control the appearance and layout of elements on a website. Thanks to its versatility, you can easily improve the aesthetics and functionality of your site. Here are the most important areas of practical application of CSS:

1. layout and page layout

CSS allows you to create page layouts by defining the placement of elements vertically and horizontally. Tools such as Flexbox and Grid Layout allow you to design flexible and responsive layouts. Example:

.container {
    display: flex;
    justify-content: center;
    align-items: center;
}

2. Text formatting

CSS allows you to change the appearance of text on a page, including its font, size, color or spacing. Example:

p {
    font-family: 'Arial', sans-serif;
    font-size: 16px;
    color: #333;
    line-height: 1.5;
}

3. Colors and backgrounds

CSS supports various color formats, such as HEX, RGB, HSL, and allows you to set images as backgrounds. You can also use gradients for interesting visual effects. Example:

body {
    background: linear-gradient(to right, #ff7e5f, #feb47b);
    color: #fff;
}

4. Visual effects

CSS allows you to add effects such as shadows, rounded corners, and animations:

• Shadows: Applied to text and elements. Example

h1 {
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.5);
}

Rounded corners: They give an aesthetically pleasing look to buttons and cards. Example:

.button {
    border-radius: 10px;
}

5. Responsiveness

CSS allows you to adjust the layout of the page to different devices thanks to media queries. Example:

@media (max-width: 768px) {
    .container {
        flex-direction: column;
    }
}

The most common mistakes and challenges in working with the CSS language

Beginners and experienced developers often encounter problems related to its cascading, specificity and scalability. Here are the most common mistakes and challenges and how to solve them:

Problems with cascading and specificity

• Problem description: CSS cascading can lead to situations where one rule unexpectedly overwrites another. Selector specificity is crucial, but its lack of understanding can cause difficulties in debugging styles. Example:

p {
    color: red;
}

#main p {
    color: blue; /* Ten styl ma wyższą specyficzność i nadpisuje poprzedni */
}

Solution:

• Avoid excessive use of nested selectors.
• Use specificity visualization tools such as DevTools in browsers.
• Consider using the BEM (Block, Element, Modifier) methodology for readability.

Conflicts in large projects

• Problem description: In larger projects, different developers may accidentally overwrite styles, leading to inconsistencies.
• Solution:
  • Introduce CSS writing methodologies such as BEM, SMACSS or OOCSS.
  • Organize styles into modular CSS files and use preprocessors such as Sass.

The complexity of debugging CSS

• Problem description: Page styling can be difficult to debug, especially when using multiple nesting or dynamic frameworks.
• Solution:
  • Use DevTools in browsers to keep track of source and style hierarchy.
  • Tag code with comments and create readable, descriptive classes.

Performance

• Problem Description: Sometimes CSS can cause performance problems, especially with complex animations or selectors acting on a large number of elements.
• Solution:
  • Avoid generic selectors such as * or tag.
  • Limit the number of complex rules (such as too many nestings).
  • Optimize animations using GPU properties such as transform and opacity.

Lack of consistency in styles

• Problem description: Manually defining styles for different elements can lead to inconsistencies.
• Solution:
  • Use CSS variables to define common values, such as colors and fonts.
  • Create global style files for reusable components.

The future of CSS

The future of CSS abounds with innovations to make web design more flexible and advanced. One key trend is Container Queries, allowing you to customize styles depending on the size of the container, revolutionizing responsive design. Enhancements, such as Subgrid, increase precision in managing layouts. The development of tools, such as the Houdini API, enables deeper customization of CSS rendering processes, opening the door to more dynamic styles. CSS is also focusing on supporting accessibility with better support for system preferences, such as dark mode and motion preferences.

Performance enhancements through animation optimization and GPU support will improve the performance of advanced visual effects. In the future, CSS will further integrate with AI technologies and component systems, making style generation faster and simpler. All these developments indicate that CSS will be a key component of modern front-end design.

Questions asked by users:

What is a CSS selector?

A CSS selector is a part of a CSS rule that indicates the HTML elements to which specific styles are to be applied.

What is the CSS language in web design?

CSS (Cascading Style Sheets) is a language used to define the appearance and layout of elements on web pages, such as colors, fonts, spacing and animations.

What is padding in CSS?

Padding is the internal space between the content of an element and its edge, defining the spacing within the element.

What is a CSS sheet?

A CSS sheet is a file with the extension .css, whichy zawiera zestaw re