What is a Progressive Web App (PWA)? How it works and when to use itA Progressive Web App (PWA) is a website built with web platform technologies that feels like a native installed app — it can be installed on a device, work offline, and run in the background. Here's how PWAs work, what they need, and when they make sense.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.What is CSS Specificity? Selectors, Specificity, and the Cascade ExplainedCSS specificity is the algorithm browsers use to pick which CSS rule wins when two declarations target the same element and property. This guide explains selectors, specificity calculation, the cascade, and inheritance — with practical examples.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.What is a Service Worker? How it works and when to use itA service worker is a JavaScript file the browser runs in the background, separate from the page. It sits between your app and the network and lets you cache assets, intercept requests, work offline, and receive push notifications. Here's how it works, what its lifecycle looks like, and when to reach for one.What is lazy loading? How deferring resources speeds up the webLazy loading is a performance strategy that defers non-critical resources (images, iframes, JavaScript, CSS) until they are needed. Learn what can be lazy-loaded, the native loading attribute, the Intersection Observer API, and when lazy loading helps or hurts. 