The overall effect is shown below:

Alright, let's walk through the steps to create this animation using CSS.

In this tutorial, we will guide you step-by-step on how to create a rotating trailing effect using CSS. We will achieve this by setting the width, height, border radius, background color, and multiple shadows for an element.

Here is the overall code and demo: https://codepen.io/venzil/pen/MWNVymY

Step 1: Setting Up the HTML Structure

First, we need to define the HTML hierarchy and structure.

The entire screen consists of three parts: first, the black background (.container), then the arc (.circle), and finally the small dot at the end of the arc (.dot).

The overall HTML structure is shown below.

<div class="container">
  <div class="circle">
    <div class="dot"></div>
  </div>
</div>

CSS Composition

1. Setting Background and Content Position

First, we set the black background of the page by directly modifying the

body {
  margin: 0;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: black;
}

By setting height: 100vh;, we ensure that the

Then, we set the size of the content.

.container {
  background-color: transparent;
  width: 200px;
  height: 200px;
}

2. Drawing the Arc and Rotating It

The first step is to form an arc, which is actually a part of a circle. Therefore, we need to draw the entire circle first.

Start by drawing a square, and the size of this square is the content size we set earlier with a side length of 200px.

.container .circle {
  border-color: yellow;
  border-style: solid;
  width: 100%;
  height: 100%;
}

Next, we use border-radius to turn the square into a circle.

.container .circle {
  border-color: yellow;
  border-style: solid;
  width: 100%;
  height: 100%;

  /* new */
  border-radius: 50%;
}

Then, we just need to clip a part of the circle to make it look like an arc.

.container .circle {
  border-style: solid;
  width: 100%;
  height: 100%;
  border-radius: 50%;

  /* new */
  border-color: yellow transparent transparent yellow;
  border-width: 3px 3px 0 0;
}

Now that the arc and the endpoint of the arc are generated, we just need to start rotating the arc.

Define a CSS animation keyframe (@keyframes) that specifies an animation sequence called animate.

In this animation sequence, the element will rotate one full turn (1turn is 360 degrees) from its initial state (usually from {}, but here it defaults to the current state).

@keyframes animate {
  to {
    transform: rotate(1turn);
  }
}

Then, apply the animation keyframe to the .circle class.

.container .circle {
  border-style: solid;
  width: 100%;
  height: 100%;
  border-radius: 50%;
  border-color: yellow transparent transparent yellow;
  border-width: 3px 3px 0 0;

  /* new */
  animation: animate 3s linear infinite;
}

1. animation: This is the shorthand property for animations, which can combine multiple values such as animation name, duration, timing function, loop count, etc.
2. animate: This is the name of the animation, corresponding to the @keyframes animate definition.
3. 3s: The duration of the animation, meaning it takes 3 seconds to complete one cycle.
4. linear: The timing function for the animation, indicating that it proceeds at a constant speed with no acceleration or deceleration.
5. infinite: The loop count, meaning the animation will repeat indefinitely.

Once set, the animation effect will appear as shown below:

Next, we can add a small dot to the rotating head to enhance the animation effect.

.container .circle .dot {
  width: 10px;                         /* Element width is 10 pixels */
  height: 10px;                        /* Element height is 10 pixels */
  border-radius: 50%;                  /* Border radius is 50%, making the element a circle */
  margin-left: 85%;                    /* Left margin is 85% of the parent element's width */
  margin-top: 13%;                     /* Top margin is 13% of the parent element's height */
  background-color: yellow;            /* Background color is yellow */
  box-shadow:                          /* Define a series of shadow effects */
    0 0 2em,                           /* The first shadow, distance 0, blur radius 0, spread radius 2em */
    0 0 4em,                           /* The second shadow, distance 0, blur radius 0, spread radius 4em */
    0 0 6em,                           /* The third shadow, distance 0, blur radius 0, spread radius 6em */
    0 0 8em,                           /* The fourth shadow, distance 0, blur radius 0, spread radius 8em */
    0 0 10em,                          /* The fifth shadow, distance 0, blur radius 0, spread radius 10em */
    0 0 0 0.5em rgba(255, 255, 0, 0.2);/* The final shadow, distance 0, spread 0.5em, yellow with transparency */
}

This is the final result: