HTML/CSS/JavaScript Fundamentals: The Core Every Developer Must Know in 2026

HTML/CSS/JavaScript Fundamentals: The Core Every Developer Must Know in 2026 Semantic HTML Matters <!-- ❌ Non-semantic --> <div class= "nav" > <div class= "item" ><a href= "/" > Home </a></div> <div class= "item" ><a href= "/about" > About </a></div> </div> <!-- ✅ Semantic --> <nav> <a href= "/" > Home </a> <a href= "/about" > About </a> </nav> Why: Screen readers, search engines, and browsers understand semantic HTML better. It's also easier to style. CSS Specificity When multiple rules target the same element, CSS specificity decides who wins: Selector Specificity Score * 0 p 1 .nav 10 #sidebar 100 style="..." 1000 !important Infinity (avoid) /* Example specificity battle */ /* Line 1: specificity = 1 */ p { color : blue ; } /* Line 2: specificity = 10 */ .nav p { color : red ; } /* WINS — specificity 10 > 1 */ /* Line 3: specificity = 100 */ #sidebar p { color : green ; } /* WINS — specificity 100 > 10 */ Rule: Keep specificity low. Avoid !important . Use BEM or CSS Modules to scope