CSS box-shadow only appears when the margin property is present

In this article, we’ll introduce the box-shadow property in CSS and explain why it only appears when the margin property is present.

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What is the box-shadow property?

The CSS box-shadow property is used to create a shadow effect around an element. It can make an element appear more three-dimensional and is often used in design to highlight elements or create special effects.

The syntax of the box-shadow attribute is as follows:

box-shadow: h-shadow v-shadow blur spread color inset; 

Where:

– h-shadow defines the horizontal offset of the shadow, which can be positive or negative;

– v-shadow defines the vertical offset of the shadow, which can also be positive or negative;

– blur defines the blur radius of the shadow; a larger value results in a blurrier shadow;

– spread defines the size of the shadow; increasing this value will expand (or shrink) the shadow;

– color defines the color of the shadow;

– inset is optional and specifies whether the shadow is an outer shadow (default) or an inner shadow.

The following example demonstrates how to use the box-shadow property to add a shadow effect to an element:

div {
width: 200px;
height: 200px;
background-color: gray;
box-shadow: 10px 10px 5px gray;
}

The above example creates a 200×200 pixel gray square and surrounds it with a gray shadow with a 10 pixel horizontal and vertical offset and a 5 pixel blur radius.

Relationship of the box-shadow Property to the Margin Property

In most cases, you don’t need to consider an element’s margins when using the box-shadow property. However, the CSS specification explicitly states that box-shadow appears above any background, border, or margin.

Suppose we have an element with a background, a border, and a margin. In this case, even if we set the box-shadow property for the element, the shadow will not appear. The box-shadow will only appear if the margin property is present and not set to its default value.

Here’s an example showing how the box-shadow property only appears when margin is not set to its default value:

div {
width: 200px;
height: 200px;
background-color: gray;
border: 1px solid black;
margin: 20px;
box-shadow: 10px 10px 5px gray;
}

In the example above, we set a 20px margin for the element and add a gray shadow with a 10px horizontal and vertical offset and a 5px blur radius. The shadow effect is visible because of the margin properties.

Suppose we remove the margin property from the above example or set it to its default value (0), the shadow will no longer appear:

div { 
width: 200px; 
height: 200px; 
background-color: gray; 
border: 1px solid black; 
margin: 0; 
box-shadow: 10px 10px 5px gray; 
} 

In the above example, since the margin property is not present, the shadow effect will not appear.

Summary

In this article, we introduced the box-shadow property in CSS and its relationship to the margin property. We learned that the box-shadow property is used to create a shadow effect around an element, but it will only appear if the margin property is present and not at its default value. This is because the CSS specification clearly states that box-shadow appears over any background, border, and margin.

A correct understanding of the relationship between the box-shadow and margin properties can help us better apply shadow effects in our designs and avoid unnecessary confusion and errors.