An HTML boilerplate provides the foundational skeleton that every web page needs to render correctly, behave responsively, and comply with modern web standards.

The HTML boilerplate sets up the basic rules so browsers can load your page correctly. If you delete it, your site will still open, but it will look glitchy on different screens.

The declaration at the very top tells the browser to parse the page using standard modern HTML5 rules. If you delete it, the browser falls into "Quirks Mode," meaning it treats your code like an outdated 1990s website. This causes modern styling features (like Flexbox, Grid, or custom margins) to render inconsistently, break your layout, and look completely different from one browser to another