CSS px detailed explanation

Using the px unit

Specifying element size

.box {
width: 200px;
height: 100px;
} 

In the above code, the width of the .box element is 200 pixels and the height is 100 pixels.

Specifying text font size

p {
font-size: 16px;
} 

In the above code, the font size of the p element is 16 pixels.

Specifying Padding and Margins

.box {
padding: 10px;
margin: 20px;
}

In the above code, the .box element has a 10-pixel padding and a 20-pixel margin.

Specifying Border Width

.box {
border: 1px solid #000;
}

In the above code, the .box element has a 1-pixel border and a black color.

Comparison of px with other units

In web development, in addition to the px unit, other units such as em, rem, and % can be used to define element sizes. Below, we compare px with these units.

Comparison of px and em units

• em units are calculated relative to the parent element’s font size. If the parent element’s font size is 16px and the child element’s font size is 1.5em, the child element’s font size is 16px * 1.5 = 24px.
• em units inherit the parent element’s font size in certain circumstances, increasing style flexibility and maintainability.
• px units are fixed pixel sizes and are not affected by the parent element’s font size.

Comparison of px and rem Units

• rem units are calculated relative to the font size of the root element (the html element). If the root element has a font size of 16px and the element has a font size of 1.5rem, the element’s font size is 16px * 1.5 = 24px.
• rem units can help developers better control the styling of the entire page, reducing dependence on the font size of the parent element.

The px unit is relative to a fixed pixel size, which may cause inconsistent display on different devices.

Comparison of px and % Units

The % unit is relative to the parent element. For example, if the parent element is 200px wide and the child element is 50% wide, the child element’s width is 200px * 50% = 100px.

The % unit is important for implementing responsive layouts, allowing elements to resize based on the parent element’s size.

The px unit is a fixed pixel size and cannot dynamically adjust based on the parent element’s size.

Conclusion

In web development, the px unit is one of the most commonly used length units. It can be used to define element sizes, padding, margins, borders, and other style dimensions. Compared to other units, the px unit may be less flexible in some situations, but in other scenarios, it is more convenient and efficient. Developers can choose the appropriate unit when defining styles to achieve optimal display effects.