How to set the height and width of an element to be the same in css

CSS (Cascading Style Sheets) is a language used to create and design web pages. In web design, it is often necessary to set the width and height of elements. These properties are very common in CSS. However, sometimes it is necessary to set the height and width of an element to be equal, which may cause some confusion for beginners. This article will introduce several methods to set the height of an element equal to its width.

The first method: use padding-top technique

This method uses the padding-top attribute to make the content height of the element equal to the width. In this technique, the padding-top property, which represents a percentage value, is set equal to the width of the element. For example, if the width of the element is 100px, the value of the padding-top attribute should be 100%.

The advantage of using this technique is that the content of the element can be flexibly adjusted to any size, and the box-sizing attribute can also be used to determine the box model type of the element. The limitation of this technique is that the padding-top attribute increases the padding at the top of the element, which may affect the layout of other elements.

The following is an example:

<div class="square"></div>

.square {
    width: 100px;
    padding-top: 100%;
    background-color: red;
    box-sizing: border-box; /* 可选，根据需要来决定盒模型 */
}

In the above example, a square div element with a width of 100px is set, with the padding-top attribute set to 100%. When the width is 100px, the value of padding-top is also 100px, making the height of the div element equal to the width, creating a square.

Second method: Use pseudo elements

The second method uses pseudo elements in CSS to convert an empty element into a square. In this technique, you create a blank element based on the padding-top attribute via the ::before or ::after pseudo-element, and then set the width and height of the element to equal values.

The following is an example:

<div class="square"></div>

.square {
    position: relative;
    width: 100px;
    height: 0;
    padding-top: 100%;
    background-color: red;
}

.square::before {
    content: "";
    display: block;
    padding-top: inherit;
}

In the above example, set a div element with a width of 100px, and set the padding-top attribute to 100%, so that the height of the div element is equal to width. An empty block-level element is created using the ::before pseudo-element, and the height of this element is also set to 100%. Use padding-top to inherit the value of the above div element so that the height and width of the empty block-level element are equal.

Third method: Use viewport units

The third method can use viewport units to create square elements. Viewport units are a unit relative to the width or height of the viewport. Use vw and vh units to determine a certain ratio of screen width and height.

The following is an example:

<div class="square"></div>

.square {
    width: 50vw;
    height: 50vw;
    background-color: red;
}

In the above example, a div element with a width of 50vw (half the viewport width) is set, and the height is also set to 50vw, thereby creating A square element.

Summary

In web design, it is often necessary to set the height and width of elements. You can accomplish this easily using CSS, and you can also use any of the three techniques above to set the height of an element to be equal to its width. Use the padding-top technique to flexibly control the content of the element, use pseudo-elements to create an empty square element, and use viewport units to determine the width and height ratio of the element. You can choose the appropriate method according to the specific situation.

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