HTML and CSS: Definition, Application, and Operating Principles

Introduction

HTML and CSS are two key tools in web development, essential for creating modern websites. HTML is responsible for the structure of a web page, while CSS is responsible for its layout and style. Together, they form the foundation of front-end development and are essential learning for anyone interested in working in web technologies.

How HTML and CSS Came to Be

Before we dive into the basics of HTML and CSS and figure out what HTML and CSS are, let’s talk about how they came to be.

• HTML (HyperText Markup Language) emerged in the early 1990s and became the foundation for creating web pages. British computer scientist Sir Timothy Berners-Lee, also known as the “Father of the Internet,” is credited with creating HTML. HTML’s basic tags and attributes allowed for the structure of a website to be defined.
• CSS (Cascading Style Sheets) was developed a little later to separate the design of an HTML website from its structure. The term was coined by Norwegian technologist Håkon Wium Lie, a colleague of Berners-Lee’s at CERN. CSS’s capabilities gradually expanded, from basic CSS styles to modern CSS functions.

What is HTML in simple terms?

HTML is the HyperText Markup Language (HTML), which is responsible for the structure of a web page. In other words, it’s the foundation without which a website couldn’t exist. HTML markup creates the website’s structure: headings, paragraphs, lists, links, images, and tables. HTML tags and attributes help the browser understand how to display the content.

An HTML document consists of various elements, each of which performs its own function:

• Headings ( <h1>– <h6>) are used to indicate headings of different levels: <h1>the most important, <h6>the least significant.
• Paragraphs ( <p>) are used to format blocks of text.
• Lists ( <ul>, <ol>, <li>) are used to create bulleted and numbered lists.
• Links ( <a href="URL">) allow you to navigate to other pages or resources.
• Images ( <img src="URL" alt="Описание">) insert graphics into the page.
• Tables ( <table>, <tr>, <td>) are used to present data in tabular form.

Learn the basics of layout for free

Take a free HTML course on our website!

How does a browser process HTML?

When you open a web page, the browser downloads the HTML code, parses it, and builds the DOM (Document Object Model)—the document structure that forms the page’s display. However, HTML alone doesn’t determine the final appearance of a website—that’s the responsibility of CSS.

What is CSS in simple terms?

CSS is a style language for designing web pages created using HTML. It controls visual presentation: colors, fonts, spacing, element placement, and even animation. When a browser loads an HTML page, it first reads its structure and then applies CSS styles to give elements the desired appearance. For example, with CSS you can define:

• Text and background color.
• Indents between elements.
• Block and image sizes.
• Fonts and their parameters.
• Animations and effects on hover.

Without CSS, web pages would look like regular documents—solid text without formatting.

Free CSS Course for Beginners

Start learning for free!

Where HTML and CSS are used

HTML and CSS are used in most web development projects. These technologies underpin everything on the internet, from simple blogs to complex web applications. Developers can use them to solve the following problems:

• Website creation. HTML is responsible for the page structure, while CSS is responsible for its design. Whether you’re building a personal blog, an online store, or a corporate website, HTML and CSS are essential. Even major platforms like YouTube and Wikipedia use these technologies.
• Working with email newsletters. Many newsletters are designed using HTML and CSS. Email services like Gmail and Outlook use special markup to display emails beautifully.
• Creating web interfaces and control panels. Most online services, such as online banking, CRM systems, or website admin panels, are developed using HTML and CSS.
• Mobile App Development. Hybrid mobile apps (built with React Native or Apache Cordova) use HTML and CSS to create an interface that adapts to different devices.
• Working with a content management system (CMS). Platforms like WordPress, Joomla, and Drupal use HTML and CSS to create and customize website templates. Understanding these technologies allows for flexible design management.

How to learn HTML and CSS?

Learning HTML and CSS is the first step in mastering web development. These languages ​​don’t require in-depth programming knowledge, so you can start learning them on your own. Here are some effective ways to quickly master the basics and learn how to create websites.

Study the theory

It’s worth starting with learning the basic concepts, key tags, and attributes. There are numerous websites online with quizzes and videos explaining HTML and CSS theory. It’s best to focus on the most recent publications, as HTML is constantly evolving and improving.

Connect to practice

The best way to remember the material is to immediately apply it. Start by creating a simple HTML document. Online sandboxes like CodePen, JSFiddle, or CodeSandbox allow you to experiment with code without installing any additional software. Later, tackle real-world tasks like coding web pages or developing a website layout in Figma.

Sign up for a free course

365education offers free courses, “HTML Basics” and “CSS Basics .” These lessons will help you master the fundamentals of these technologies and take your first steps in front-end development.

Practical tips for working with HTML and CSS

Mastering HTML and CSS isn’t just about tags and styles. It’s about writing clean and easy-to-use code. Here are the basic principles of good layout that help you create high-quality web pages.

1. Use semantic markup

HTML isn’t just a way to place text and images on a page. It helps search engines and browsers understand the role of elements. Instead of <div>using semantic tags for everything:

• <header>— for the website header,
• <nav>— for the navigation menu,
• <article>— for articles,
• <section>— for sections,
• <footer>— for the page footer.

This approach improves SEO and makes the code clearer.

2. Separate markup and styles

Never write styles directly in HTML (e.g., style=”color: red;”). Instead, include a separate CSS file. This makes the code cleaner, easier to maintain, and allows you to change styles in all files at once.

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

3. Work with a grid system and responsiveness

Use CSS Grid or Flexbox to position elements on the page. These technologies allow you to create responsive layouts. Responsiveness is crucial. Use max-width instead of width, relative units (em, %, vw, vh) instead of pixels, and media queries:

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

This way, your website will look good on both computers and phones.

Avoid unnecessary animations and don’t use too many fonts and unoptimized images. Minify CSS and combine files to reduce the number of server requests.

4. Make your code readable

Clean code is important not only for other developers but also for your own future. Follow these rules:

• Indents (use 2 or 4 spaces, not tabs).
• Class names are descriptive, not div1, div2. Better menu-item, footer-links.
• Grouping properties: first positioning, then styling.

Check the code before publishing

Before you upload your site, test it:

• In different browsers (Chrome, Firefox, Safari).
• On mobile devices.
• Through validators ( W3C Validator for HTML, CSS Validator ).

CSS Basics in a Free Course

Your start in layout !

Conclusion

Although HTML and CSS aren’t programming languages ​​in the traditional sense, they’re essential for creating a modern website. Learning them is the first step into the world of front-end development. By mastering the basic principles of markup and styling, you’ll be able to create responsive, user-friendly, and beautiful websites.

Explore More IT Terms