Mastering CSS `outline`: Adding Visual Emphasis to Webpage Elements

Learn how to use the CSS `outline` property to effectively add visual emphasis to elements without affecting their dimensions. This tutorial compares `outline` with `border`, demonstrates various outline styles and the `outline-offset` property, and provides best practices for using `outline` in your web designs.

Styling with CSS `outline`

What is CSS `outline`?

The CSS `outline` property adds a line around an element, similar to a border, but with key differences. It's useful for drawing visual attention to an element or for adding a stylistic emphasis. The outline sits outside the element's border, padding, and margin.

`outline` vs. `border`

While both borders and outlines create lines around elements, there are important distinctions:

  • Customization: The `border` property allows for individual styling (width, style, color) for each side of the element (top, right, bottom, left), while `outline` applies the same values to all four sides.
  • Dimensions: The `border` is part of an element's dimensions, increasing its overall size. The `outline` doesn't affect an element's dimensions; it's drawn outside the element's box.
  • Shorthand Property: `outline` is a shorthand for `outline-width`, `outline-style`, and `outline-color`. You can use any of these individually as well.

`outline` Properties

  • outline-width: Sets the outline's thickness (keywords: thin, medium, thick; or length units).
  • outline-color: Specifies the outline color (using any valid CSS color format).
  • outline-style: Defines the outline style (none, dotted, dashed, solid, double, groove, ridge, inset, outset).

Example: Different Outline Styles

This example showcases different outline styles. You would need to include corresponding HTML elements (e.g., divs) to see these styles in action.

CSS Code

div {
  width: 100px;
  height: 50px;
  margin-bottom: 10px;
}

div:nth-child(1) { outline-style: dashed; }
div:nth-child(2) { outline-style: dotted; }
div:nth-child(3) { outline-style: double; }
div:nth-child(4) { outline-style: groove; }
div:nth-child(5) { outline-style: inset; }
div:nth-child(6) { outline-style: outset; }
div:nth-child(7) { outline-style: ridge; }
div:nth-child(8) { outline-style: solid; }

`outline-offset` Property

The `outline-offset` property creates space between the outline and the element's border. The space between the border and the outline will be transparent and will take on the background color of the parent element. This makes the outline visually distinct from the border.

Conclusion

The `outline` property offers a flexible way to add visual emphasis to elements without affecting their dimensions. While similar to the `border` property, understanding their differences is vital for creating effective and well-structured layouts. Remember that the `outline` property is applied outside the element's box, unlike a border.