How to Create a CSS Div with Height Equal to its Dynamic Width?

Height Matching Dynamic Width: A CSS Fluid Layout

Aiming to achieve a visually balanced design, developers often seek to align the height of an element to its width. This question addresses a common design challenge: how to create a div with a height equal to its width, maintaining a 1:1 aspect ratio while allowing the width to vary dynamically.

A proposed solution involves the use of a placeholder element with a predefined aspect ratio. By placing the main element within the placeholder, the aspect ratio is maintained even as the width of the main element changes. The key lies in leveraging CSS properties like position and margin-top to strategically align the elements and ensure their dimensions remain proportionate.

The following code snippet demonstrates the approach:

#container {
  display: inline-block;
  position: relative;
  width: 50%;
}

#dummy {
  margin-top: 75%;
  /* 4:3 aspect ratio */
}

#element {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: silver/* show me! */
}

In this example, the #container establishes the dynamic width of the div. The #dummy element is used as a placeholder with a fixed 4:3 aspect ratio, achieved through the margin-top property. The #element is then positioned absolutely within the #dummy, ensuring that it fills the entire area and maintains the same 1:1 ratio as the width.

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