How to optimize images for the web: formats, resizing, lazy loading, and CLSImages are usually the heaviest assets on a page. Here's how to pick the right format, serve the right size, lazy-load what's offscreen, and stop images from shifting your layout.What is web accessibility (a11y)? WCAG principles and practical techniquesWeb accessibility (a11y) means designing sites that anyone can use, regardless of ability. This guide explains the four WCAG principles — perceivable, operable, understandable, robust — and practical techniques: semantic HTML, keyboard navigation, alt text, and color contrast.Flexbox vs Grid: which CSS layout should you choose?Flexbox and CSS Grid are two layout systems built into the browser. Flexbox is one-dimensional (a row or a column); Grid is two-dimensional (rows and columns at once). Learn how each one works, when to reach for it, and how to combine them.What is HTML? How HyperText Markup Language works and why it mattersHTML is the foundation of every web page. Learn what HyperText Markup Language is, how HTML elements and tags work, why semantic HTML matters for SEO and accessibility, and how HTML fits with CSS and JavaScript.What is responsive web design? How it works (media queries, fluid grids, images)Responsive web design (RWD) makes pages render well on every screen size. Learn how media queries, fluid grids, fluid images, and the viewport meta tag work together. 