I think this is the answer you are looking for:
In HTML and CSS, the body element, by default, takes up the entire height of the viewport, even if its content has zero or minimal height. This behavior is a result of the default styles applied by browsers.
Here's why the body background color fills the whole screen even if it has zero height:
Default Styles: Browsers have default styles for HTML elements, including the body. By default, the body element has a margin of 8px, which can create spacing around the body content. Additionally, the body has default padding and border values set to 0.
Collapsing Margins: In CSS, margins of adjacent elements can sometimes "collapse" into each other, causing the effective margin to be larger. If there is no content or explicit padding or margin set on the body, the margin might collapse to the html element, causing the body to extend to the top of the viewport.
Viewport Height: The body element is expected to fill the entire viewport by default. If it has no content or minimal content with no explicit height, it will still expand to occupy the full height of the viewport.
To prevent this behavior and make the body element take only as much height as its content, you can explicitly set the height of the body to auto in your CSS:
body { height: auto; /* Other styles */ }
Or, if you want to ensure the body element only takes the height of its content and has no margin, you can use:
body { margin: 0; height: auto; /* Other styles */ }
By setting height to auto, you instruct the browser to adjust the height of the body based on its content, and by setting margin to 0, you remove any default margin that might be collapsing with other elements.