To define a simple CSS transition, use the transition attribute and specify the transition attribute, duration, and optional behavior. 1. Select commonly used animated properties such as color, background-color, opacity, transform and width; 2. Avoid trying non-animated properties such as display or content; 3. Use browser developer tools to quickly test the transition effect; 4. The basic transition needs to specify at least the transition attributes and duration, and you can also add time functions and delays; 5. When you need to respond to the end of the transition in JavaScript, use the transitionend event and pay attention to cleaning up the event listener. By focusing on one or two attributes and basic time settings and expanding as needed, you can keep the transition effect simple and effective.

Defining a simple CSS transition is straightforward — it's about making a property change smoothly over time instead of snapping instantly from one state to another. The key is using the transition property (or its longhand equivalents) and specifying what you're transitioning, how fast, and optionally, how it behaves during the transition.

What properties can you transition?

Not all CSS properties are animalable, but most commonly used ones like color , background-color , opacity , transform , and width are. You don't have to guess — just try it out or refer to a list of animalable properties .

• Stick to know animatable properties for reliable results
• Avoid trying to animate non-animatable properties like display or content
• Use browser dev tools to test transitions quickly

If you're unsure whether a property will work, write the transition and see what happens in the browser. It's often the fastest way to find out.

How to set up a basic transition

To define a simple transition, you need at least two things: which property you want to transition and how long the transition should take. Here's a minimal example:

 .box {
  width: 100px;
  transition: width 0.3s;
}

.box:hover {
  width: 200px;
}

This tells the browser to animate the width change over 0.3 seconds whenever it changes — like when hovering over the element.

You can also use shorthand to include timing functions and delays:

 transition: width 0.3s ease-in-out 0.1s;

This adds a smooth acceleration/deceleration and a slight delay before starting.

When should you use transitionend ?

If you're doing something in JavaScript after a transition completes — like removing a class or triggering another animation — you'll want to listen for the transitionend event.

• Use it when you need to react to the end of a visual transition
• Be aware that it fires once per animated property , so you may want to debounce or check which property finished
• Always clean up event listeners if they're only needed once

For example:

 const box = document.querySelector('.box');

box.addEventListener('transitionend', () => {
  console.log('Transition finished');
});

It's not always necessary, but it becomes handy when coordinating transitions with JS behavior.

Basically that's it. Keep it simple by focusing on one or two properties, start with basic timing, and expand as needed.

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