How to Create an Animated Circle with a Transparent Background and Rounded Border?

Drawing a Circle with Transparent Background and Animate Border Radius

You seek to create a circle with a rounded border and animate it while preserving the transparency of the background. The challenge lies in achieving this without revealing the masked portion before the animation begins.

Solution:

Here's a proposed solution:

1. Establish a transparent background: Set a repeating linear gradient on the body element to provide a visible indication of transparency.
2. Create a container: Define a container that positions the circle absolutely and provides dimensions.
3. Define the half-circle clip: Introduce a halfclip element that conceals one half of the circle. Position it absolutely within the container, setting its transform-origin to the center-left corner. Apply an animation to rotate the halfclip clockwise in steps.
4. Create a hollow semi-circle: Define a halfcircle element with a hollow center and blue borders. Position it absolutely within the halfclip, using CSS animation to rotate it linearly between -45 degrees and 135 degrees.
5. Add a fixed semi-circle: Include a second halfcircle element, positioned absolutely with an initial rotation of 135 degrees. This element will create the appearance of the animation starting from a complete circle.

By incorporating these elements, you can achieve the desired animation of a circle drawn with a rounded border while ensuring the background remains transparent.

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