How Can I Animate the Width of a CSS Element with `width: auto`?

Animating Width of Content with width: auto

One common challenge in CSS is animating the width of an element when its contents change. This can be tricky, especially when the element has width: auto, which prevents specifying an explicit width.

The traditional solution is to use the transition property to animate between two specific width values. However, this approach doesn't work well for content that can vary in length, as it requires manually setting the width values that the element can transition between.

As the commenter mentioned, it's currently not possible to directly animate the width: auto property. One workaround is to utilize the max-width and max-height properties. By providing a large enough maximum width for the content, we can ensure that it will always fit, even when expanded.

Here's an example of the "max-width" trick:

.myspan {
  display: inline-block;
  font-size: 30px;
  background-color: #ddd;
  vertical-align: bottom;
}
.myspan::after {
  content: " a0\f12a ";
  font-family: ionicons;
  font-size: 80%;  
  display: inline-block;
  max-width: 0;
  transition: max-width .6s;
  vertical-align: bottom;
  overflow: hidden;
}
.myspan:hover::after {
  max-width: 80px;
  transition: max-width 1s;
}

Here, we implement a "flush" animation when the mouse hovers over the element. The content remains fixed at 30px, while the icon slides out smoothly using the max-width animation.

If greater precision is desired, a JavaScript solution can be employed. This involves dynamically setting the element's width based on the length of its content. While this approach provides more control, it comes with the added complexity of JavaScript implementation.

In summary, while animating width: auto directly is not yet possible, workarounds like the "max-width" trick or JavaScript scripts can be used to achieve the desired effect.

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