How to Animate Variable Fonts CSS?

The simplest and most common way to animate variable fonts in CSS is by using CSS @keyframes. This method allows you to create simple and smooth animations directly within your stylesheets.

Understanding Variable Fonts and Animation

Variable fonts are modern font files that contain multiple variations of a typeface within a single file. Instead of needing separate files for bold, light, condensed, etc., you can access a continuous range of styles by adjusting specific "axes" of the font. Common axes include weight (wght), width (wdth), slant (slnt), and italics (ital), but designers can also create custom axes.

Animating variable fonts means smoothly transitioning the value of one or more of these axes over time. For example, you could animate the wght axis to make text gradually appear bolder or lighter.

Animating with CSS @keyframes

As mentioned in the reference, CSS @keyframes provide the most straightforward approach for animating variable font properties. This technique involves defining keyframes that specify the style of an element at various points during an animation sequence (e.g., at 0%, 50%, 100%).

The primary CSS property you'll animate is font-variation-settings. This property controls the values of the font's variation axes using a comma-separated list of axis tags and their desired values.

Steps to Animate Variable Fonts using @keyframes:

Define the @keyframes Rule: Create an @keyframes rule with a unique name. Inside this rule, define the styles at different percentages of the animation duration (typically 0% and 100% for simple transitions).
Specify font-variation-settings: Within the keyframes, set the desired font-variation-settings property to change the variable font axes.
Apply the Animation: Apply the defined animation to the HTML element containing the text using the animation CSS property (or its longhand properties like animation-name, animation-duration, animation-iteration-count, etc.).

Example: Animating Font Weight

Let's demonstrate how to animate the font weight (wght) axis of a variable font:

/* 1. Define the @keyframes rule */
@keyframes pulseWeight {
  0% {
    /* Start state: normal weight */
    font-variation-settings: 'wght' 400;
  }
  50% {
    /* Mid-state: bolder weight */
    font-variation-settings: 'wght' 700;
  }
  100% {
    /* End state: back to normal weight */
    font-variation-settings: 'wght' 400;
  }
}

/* Apply the animation to an element */
.animated-text {
  font-family: 'YourVariableFontName', sans-serif; /* Make sure to use a variable font */
  font-size: 2em;
  /* 2. Apply the animation properties */
  animation-name: pulseWeight;
  animation-duration: 3s; /* Animation lasts 3 seconds */
  animation-timing-function: ease-in-out; /* Smooth acceleration/deceleration */
  animation-iteration-count: infinite; /* Repeat indefinitely */
}

In this example:

We define @keyframes pulseWeight that transitions the 'wght' axis value from 400 to 700 and back to 400.
The .animated-text class applies this animation. It specifies the font family (crucially, it must be a variable font), the animation name (pulseWeight), duration (3s), timing function (ease-in-out), and iteration count (infinite).

Benefits of using CSS @keyframes

Simplicity: It's a native CSS feature and doesn't require JavaScript for basic animations.
Smoothness: CSS @keyframes create simple and smooth animations, as highlighted in the reference. The browser handles the interpolation between keyframes efficiently.
Performance: CSS animations are often hardware-accelerated by the browser, leading to better performance compared to some JavaScript animation methods.

While CSS @keyframes can't be controlled as dynamically or easily as animations driven by JavaScript (e.g., pausing, scrubbing, or reacting to complex user interactions), they work effectively for most visual flourishes and continuous animations.

Using CSS @keyframes is the simplest and most effective way to add smooth, style-based movement to your variable fonts directly within your stylesheets.

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