How to achieve circular effect in css

CSS is a style sheet language we often use in web development. It can achieve many interesting page effects, such as rounded corners, gradients, animations, etc. In this article, we’ll look at how to achieve a circular effect using CSS.

In CSS, we can use the border-radius property to set the rounded corners of an element. This property accepts one or more values ​​representing the corner radius of the upper left corner, upper right corner, lower right corner, and lower left corner respectively. If only one value is set, it means that the four corners are equal. If two values ​​are set, the first represents the radius in the horizontal direction and the second represents the radius in the vertical direction. If three values ​​are set, the first represents the radius of the upper left and lower right corners, the second represents the radius of the lower left and upper right corners, and the third represents the radius in the vertical direction. For example, the following code will set a div element to a circle with a width and height of 100 pixels.

div{
  width: 100px;
  height: 100px;
  border-radius: 50%;
}

In this code, the value of border-radius is 50%, which means that the four corners are set to have a radius of half the width and height of the element, resulting in a circle.

In addition to using the border-radius attribute, we can also use pseudo-elements ::before and ::after to achieve a circle. We can set a square element to have equal width and height and then convert it to a circle using the ::before or ::after pseudo-elements. For example, the following code will set a div element using the ::before pseudo-element to a circle with a width and height of 100 pixels.

div{
  width: 100px;
  height: 100px;
  position: relative;
}
div::before{
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: inherit;
  height: inherit;
  border-radius: 50%;
}

In this code, we set the div element to relative positioning, and then use the ::before pseudo-element to absolutely position the upper left corner of the div element. The pseudo-element's width and height are inherited from the div element, and its corner radius is set to 50% using the border-radius property, resulting in a circle.

Alternatively, we can also use the transform property in CSS3 to rotate the square element 45 degrees, and then use the overflow:hidden property to crop it into a circle. For example, the following code will set a div element to a circle with a width and height of 100 pixels.

div{
  width: 100px;
  height: 100px;
  transform: rotate(45deg);
  overflow: hidden;
}
div::before{
  content: "";
  display: block;
  width: 200%;
  height: 200%;
  margin: -50%;
  background-color: #000;
  border-radius: 50%;
}

In this code, we rotate the div element 45 degrees and crop its four corners using the overflow:hidden attribute. We then use the ::before pseudo-element to generate a circle that takes up the entire element and move it to the center point of the div element, resulting in a circle.

In short, CSS provides a variety of methods to achieve circular effects, including using the border-radius property, pseudo-elements, and transform properties. In actual projects, we need to choose the appropriate method according to specific scenarios and needs to achieve the desired effect.

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