html - Make div full size of window with NO margin - Stack Overflow

I hate to even ask something that seems so dumb but I just dont get this. All I want to do is have a blue div at the top of my window that stretches across the entire window. I thought width:100%;

How to Make a Child Div Element Wider than Parent Div using CSS ? - GeeksforGeeks

How to Set CSS Margins and Padding, and Cool Layout Tricks

Overflow · Bootstrap v5.0

How to make div fill full height of parent in Tailwind CSS ? - GeeksforGeeks

How to make div width expand with its content using CSS ? - GeeksforGeeks

How to find the width of a div using vanilla JavaScript? - GeeksforGeeks

CSS Height Full Page: CSS gotcha: How to fill page with a div? - DEV Community

Rendering large lists with React Virtualized - LogRocket Blog

How the Bootstrap Grid Really Works, by Carol Skelly, WDstack

html - Make Div Element 100% Height of Browser Window Using CSS - Stack Overflow

Expand side elements outside fixed width container, by Javier Villanueva

Why rows are higher than other rows on css grid - HTML-CSS - The freeCodeCamp Forum