Why Does Styling the Body Element's Background Affect the Entire Screen?

The Mysterious Effect of Styling the Body Element's Background

When applying styles to the background of the body element, developers may encounter an unexpected phenomenon where the styling extends beyond the element itself, affecting the entire screen. This behavior stems from the inherent nature of the body element's relationship with the website's canvas.

According to the CSS spec at w3.org/TR/CSS21/colors.html, the background property of the root element, which is the body element, "becomes the background of the canvas and covers the entire canvas." As a result, it acts as the backdrop for the entire web page, anchoring itself to the root element's position.

In practical terms, when the body element's background is styled, the original background disappears, and the new style is applied to the entire screen. This occurs regardless of any other dimensions or styling applied to the body element itself. In the example provided, the border of the body element remains visible within the 700px width, while the background color encompasses the entire browser viewport.

Thus, the apparent expansion of styling beyond the body element itself is a consequence of the body element's role as the root element and its interaction with the web page canvas.

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