Summary  
This chapter explains how to use the CSS `transition-duration` property to specify the length of time (in seconds or milliseconds) over which a transition effect occurs.  

General domain of usage  
Web user interface styling and animations

We use the `transition-duration` property to specify the time during which the transition should occur. This property is expressed in seconds (e.g., `3s` or `0.45s`) or milliseconds (e.g., `3000ms` or `450ms`). When the duration of a transition is not explicitly defined, the change happens instantaneously.
```css
transition-duration: 3s | 3000ms;
```

Let's run the following example to see what behaviors we can get. Please, hover over the container, and the transition will start for all elements. The difference is in the duration of the transition.

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Which of the following is a valid unit for expressing the `transition-duration` property?

Level up your styling skills by mastering advanced CSS techniques for modern web design. Position and manage elements with precision using advanced positioning strategies. Create smooth transitions and engaging animations to enhance user experience. Transform and manipulate elements for dynamic visual effects. Build responsive designs that adapt across devices and learn to streamline your workflow with CSS preprocessors like Sass.

Research what learners can expect from this advanced HTML and CSS styling course. What do you need to know before starting the course? What topics will be covered in it?

Position and manage elements on the web pages. Learn about the different positioning properties, discover how to use the stacking order to control the visibility of elements that overlap each other, and finally, handle content overflow. 

Research the power of transitions and learn how to improve the user experience. Discover how to liven properties smoothly and gradually, creating seamless state transitions.

Learn about the animation property and how it can be used to create dynamic and engaging designs. Discover how to create complex animations using keyframes and how to control the animation.

Explore the transformation property, which allows modifying the appearance and position of elements on a webpage. Learn how to scale, rotate, skew, and translate elements in two and three dimensions. Combine multiple transformations to create more complex effects.

The principles and techniques used in adaptive/responsive design aim to make websites and applications accessible and visually appealing across different devices, screen sizes, and orientations.

Learn about preprocessors in CSS and how they can help to write more efficient and maintainable code. Understand how to use preprocessors to simplify the workflow and generate cleaner CSS code.

Setting Transition Duration for Effects