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What are HTML5 and CSS?

What are HTML5 and CSS?

  • 2025-09-03

HTML5 and CSS are essential foundational technologies for modern website development . Together, they form the “framework” and “look and feel” of a website, making them essential core languages ​​that every web designer and front-end developer must master.

What is HTML5?

HTML5 , the full name of which is HyperText Markup Language 5, is the fifth-generation standard of HTML (Hypertext Markup Language ), jointly promoted and developed by the World Wide Web Consortium (W3C) and WHATWG (Web Hypertext Application Technology Working Group).

The main function of HTML5 is to structure web page content , that is, to define the various elements of a website, such as titles, paragraphs, pictures, videos, tables, links, etc.

Important features of HTML5:

  1. New semantic tags
    • For example <header>, <footer>, <article>, <section>, <nav>, make the web page structure more meaningful, which helps SEO optimization and readability.
  2. Multimedia support
    • Native support <audio>and <video>tags allow you to embed music and videos without plug-ins.
  3. Form Enhancement
    • Add new form control types, such as <date>, <email>, <url>and provide more powerful validation functions.
  4. Canvas and SVG drawing
    • By <canvas>combining elements with JavaScript, you can dynamically draw 2D graphics, games, or data visualizations.
  5. Local Storage (Web Storage)
    • Contains localStorageand sessionStorage, allowing websites to store data on the user side, replacing the previous cookies.
  6. Stronger cross-platform and device support
    • It is especially optimized for mobile devices (mobile phones and tablets) to better support responsive design.

What is CSS?

CSS , whose full name is Cascading Style Sheets , is a language used to control the appearance of HTML files .

Simply put, HTML is responsible for “content” and “structure,” while CSS is responsible for “design” and “beautification.”
Using CSS, you can easily set the visual details of a web page, such as fonts, colors, layout, margins, animation effects, and more.

The main functions of CSS are:

  1. Style and layout control
    • Set the font, background, border, margin/padding, etc.
  2. Layout
    • Use technologies such as Flexbox and Grid to achieve adaptive and responsive web design.
  3. Media Queries
    • Dynamically change the website layout and style based on the device’s screen size or resolution to enhance the user experience.
  4. Animation and Transition
    • Use CSS Animation or Transition to create smooth dynamic effects and enhance the sense of interactivity.
  5. Variables and Modularization
    • CSS supports custom variables (Custom Properties), which can improve the maintainability and consistency of large-scale website development.

The relationship between HTML5 and CSS

  • HTML5 is responsible for defining “what content is on a website.”
  • CSS is responsible for defining how this content should be presented.

The two work together to ensure that the website is not only complete in content, but also has a beautiful layout and a smooth user experience.
For example, the title of an article on a website is marked with HTML <h1>, while its font size, color, and spacing are set by CSS.

Why is it important to learn HTML5 and CSS?

  1. The foundation of website building
    • Whether it is a simple personal website or a large e-commerce platform, HTML5 and CSS are indispensable.
  2. SEO optimization
    • Using the correct HTML semantic tags can make it easier for search engines to understand the content and improve rankings.
  3. Improve user experience
    • Good CSS design can make the website load quickly, have a clear layout, and be smooth to use, thereby improving retention and conversion rates.
  4. The cornerstone of front-end technology
    • To further learn advanced front-end technologies such as JavaScript, React, Vue, etc., the basics of HTML5 and CSS are essential.

summary

HTML5 and CSS are the soul of modern website development, neither of which can be achieved without them. Mastering them not only allows you to create visually appealing and clearly structured websites, but also lays a solid foundation for learning more complex front-end frameworks. Whether you’re planning to build your own website, become a front-end developer, or improve your SEO, a deep understanding of HTML5 and CSS is a skill worth investing in!