Why Does Overflow Hidden Prevent Floating Elements from Escaping Their Container?

Floating elements can sometimes extend beyond their container's boundaries, leading to undesirable page layouts. One effective solution to this issue is to set the 'overflow' property of the container to 'hidden.' While this works well in practice, its underlying mechanism can be puzzling.

To understand the behavior, we need to consider the concept of block formatting contexts (BFC). When 'overflow' is set to 'hidden,' the container establishes a BFC. BFCs have significant implications for floats and clearing.

Specifically, within a BFC, floats only affect the layout of other elements within that BFC. They do not extend beyond its boundaries or interfere with elements outside of it. This ensures that the floating elements remain contained within their intended space.

Moreover, the 'clear' property only applies to floats within the same BFC. Setting 'overflow' to 'hidden' creates a BFC and effectively isolates the floating elements from any external influences. As a result, they are prevented from escaping their container.

By establishing a BFC, 'overflow: hidden' provides a clean and cross-browser solution for preventing floated elements from encroaching on neighboring elements. It maintains a well-structured page layout without the need for additional markup or complex workarounds.