CSS outline vs border

In CSS, both outline and border are used to create visual boundaries around elements, but they have different purposes and behaviors. Here’s a detailed comparison of outline and border:

CSS border

The border property adds a line around an element’s box. It is part of the element’s box model, which affects the layout and spacing of the element.

Key Points:

• Placement: Borders are placed inside the element’s padding and affect the element’s size and layout.
• Size Impact: Borders add to the element’s total width and height, which can affect the surrounding layout.
• Properties: Borders have width, style, and color properties.
  • Width: Defines the thickness of the border (border-width).
  • Style: Defines the style of the border line (e.g., solid, dotted, dashed).
  • Color: Defines the color of the border (border-color).

Example:

Usage in HTML:

In this example, the div will have a solid black border that is 2 pixels wide.

CSS outline

The outline property is used to draw a line around an element, but it does not affect the element’s layout or size. It is generally used for focus indicators and accessibility enhancements.

Key Points:

• Placement: Outlines are drawn outside the element’s border and do not affect the layout or size of the element.
• Size Impact: Outlines do not change the element’s dimensions or the layout of surrounding elements.
• Properties: Outlines have width, style, and color properties.
  • Width: Defines the thickness of the outline (outline-width).
  • Style: Defines the style of the outline line (e.g., solid, dotted, dashed).
  • Color: Defines the color of the outline (outline-color).

Example:

Usage in HTML:

In this example, the div will have a red outline that is 2 pixels wide, without affecting its size or layout.

Comparative Summary

• Effect on Layout:
  • border: Affects the element’s box model; increases the element’s width and height.
  • outline: Does not affect the element’s size or layout; drawn outside the border.
• Use Cases:
  • border: Used for defining the visual boundary of elements and can affect the element’s layout and spacing.
  • outline: Commonly used for accessibility purposes, such as focus indicators, without affecting the layout.
• Inheritance:
  • border: Can be inherited by child elements in certain cases.
  • outline: Does not affect child elements; generally used independently.

Combined Example

You can use both border and outline on the same element to achieve different visual effects:

Usage in HTML:

In this example, the div will have a blue border and a red dashed outline, showing how both properties can be used together for styling purposes.

Accessibility Considerations

• Focus Indicators: Outlines are often used to provide visual feedback for focused elements, especially in forms and interactive elements, enhancing accessibility for keyboard users.
• Customizable: Borders can be styled to match design requirements but may sometimes hide focus indicators if not used thoughtfully.