Creating smooth entry animations can be challenging. The complexities of DOM load times and animating from display: none often lead to frustrating results. The @starting-style rule offers a streamlined solution by allowing you to explicitly define initial values for CSS properties when an element first appears, ensuring seamless transitions from the start.

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Understanding the Fundamentals

@starting-style sets the initial state of your CSS properties before the element becomes visible—its "before" state. The "after" state is defined in your standard CSS rules. Here's how it works:

element {
  transition: opacity 0.5s ease-in;
  opacity: 1;

  @starting-style {
    opacity: 0;
  }
}

Upon initial load, @starting-style sets the element's opacity to 0. It then smoothly transitions to the final state (opacity: 1 in this case). This functionality also applies when an element transitions from display: none to visible, making it perfect for animating toggled elements.

Utilizing @starting-style

You can apply @starting-style in two ways: nested within an element's ruleset (no selector needed) or defined separately with a selector.

Important Note: Nesting @starting-style within a pseudo-element (like ::before or ::after) won't work as intended. The styles will affect the parent element, not the pseudo-element.

/* Standalone */
@starting-style {
  element {
    opacity: 0;
  }
}

element {
  opacity: 1;
  transition: opacity 0.5s ease-in;
}

/* Nested */
element {
  opacity: 1;
  transition: opacity 0.5s ease-in;

  @starting-style {
    opacity: 0;
  }
}

Key Consideration: @starting-style and the "original rule" have equal specificity. For reliable application, always place the @starting-style at-rule after the "original rule."

Practical Applications

@starting-style excels at creating entry effects and transitions. Consider its use for fading in text on page load or animating popups and dialogs. Here are a couple of examples:

Animating from display: none

The primary benefit of @starting-style is its ability to create smooth transitions for initially hidden elements, particularly those transitioning from display: none. Without @starting-style, animating this transition is difficult due to the lack of a defined starting state. @starting-style solves this by providing that initial state.

A dialog element provides a clear illustration. Its body toggles between display: none and display: block. Animating this usually isn't possible because of the display property change, but @starting-style makes it achievable.

Fading and Sliding on Page Load

In this example, @starting-style defines the "before" state for both elements. The fade effect sets initial opacity to 0, while the slide effect uses a left translation.

This article focused on entry animations. Exit effects are not handled by @starting-style. For exit animations, you'll need to explore transition-behavior, a topic for another discussion.

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