HTML5 semantic tags — <header>, <main>, <article> — give your page clear meaning and structure. They matter for SEO and screen readers alike. As browsers fully support these tags, the old <div id="header"> approach is fading out.
CSS3 Flexbox and Grid let you build complex layouts with minimal code. Custom properties (CSS variables) make design systems much easier to maintain. Media queries ensure your single codebase looks great on every device.
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