CSS transitions enable switching between CSS attribute values ??through smooth animations, which are suitable for user interaction scenarios such as button hovering effects, menu expansion and collapse. Common usages include button closure effect, drop-down menu gradient, background color gradient, image transparency or zoom changes. The basic syntax is transition: attribute duration timing function, which can specify a single or multiple attributes, or all can be used to represent all attributes, but be used with caution. Timing functions such as ease, linear, and ease-in-out control the animation speed curve, and can also be customized by cubic-bezier. It is recommended to prioritize opacity and transform for better performance, and combine @media (prefers-reduced-motion) to improve accessibility. Be careful to avoid skipping frames when operating JavaScript.

CSS transitions let you smoothly animate changes between CSS property values, instead of having them switch instantly. They're commonly used for things like hover effects, button states, or UI feedback — basically anywhere you want a visual change to feel more natural and poisoned.

When to Use Transitions

Transitions work best when you're changing properties on user interaction (like :hover , :focus , or JavaScript-triggered class changes). For example, making a button slightly grow when hovered over, or fading in a dropdown menu.

They're not mean for complex animations — that's where keyframe animations come in. But for simple state changes, transitions are lightweight and easy to set up.

Here are some common use cases:

• Button hover effects
• Expanding/collapse menus
• Changing background colors gradually
• Image opacity or scale on interaction

Basic Syntax

To create a transition, you usually define two things: which property to animate and how long the animation should take. The most basic syntax looks like this:

 transition-property: width;
transition-duration: 0.3s;

Or you can shorthand it:

 transition: width 0.3s ease;

You can also specify multiple properties by separating them with commas:

 transition: width 0.3s ease, background-color 0.5s linear;

And if you want all properties to transition, just write:

 transition: all 0.3s ease;

Just be careful with all — it can sometimes cause unintended animations on properties you didn't expect.

Controlling Transition Timing

Timing matters a lot in how smooth and natural your transitions feel. You can adjust both duration and timing function.

Duration is straightforward — it's how long the transition takes. Too short (like 0.1s) feels jarring; too long (like 2s) might frustrate users.

Timing functions control the speed curve of the transition. Common ones include:

• ease – starts slow, speeds up, then slows again (default)
• linear – constant speed from start to finish
• ease-in – starts slow, ends fast
• ease-out – starts fast, ends slow
• ease-in-out – symmetric acceleration/deceleration

For fine-tuning, you can use cubic-bezier curves to create custom timing curves. Tools like cubic-bezier.com help visualize them.

Tips for Smooth Transitions

Not all CSS properties animate well — stick to things like opacity , transform , and background-color for best performance. Avoid animating layout properties like width or height unless necessary, since they can trigger reflows.

Also, consider accessibility. Some users may prefer reduced motion, so you can add this to respect their preferences:

 @media (prefers-reduced-motion: no-preference) {
  /* your transitions here */
}

Another small but useful trick: if you're toggling classes via JavaScript, make sure the browser has time to register the initial state before triggering the transition. Sometimes a tiny delay ( requestAnimationFrame ) helps avoid skipped frames.

Basically that's it.

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