How to set width and height in css

In web development, setting the width and height of elements is a very important task. There are many ways to set width and height in CSS. This article will discuss and introduce the technology of setting width and height in CSS.

1. Basic method: use the width and height attributes

The most basic method is to use the width and height attributes in CSS. Use this attribute to simply specify the width and height of an element, for example:

div {
    width: 200px;
    height: 100px;
}

In this example, we specify a div element with a width of 200 pixels and a height of 100 pixels. It should be noted that although the default unit of the width and height attributes is pixels (px), other units such as em, rem, and percentage can also be used.

2. Using the max-width and max-height attributes

Sometimes, we want the size of an element not to exceed a specific value. In this case, we can use max-width and max-height properties to achieve this. For example:

img {
    max-width: 100%;
    max-height: 100%;
}

In this example, we set the maximum width and maximum height of an image to 100%. This means that when the image ratio exceeds 1:1 (that is, the aspect ratio is not 1), the height of the image will be adaptively reduced to maintain the aspect ratio.

3. Using the min-width and min-height attributes

Sometimes, we want the size of an element not to be smaller than a specific value. In this case, we can use the min-width and min-height properties to achieve this. For example:

div {
    min-width: 500px;
    min-height: 200px;
}

In this example, we specify that the minimum width of a div element is 500 pixels and the minimum height is 200 pixels. If the element content is too small, it will automatically grow to meet the minimum size requirement.

4. Use vh and vw units

When designing web pages, sometimes we want to set based on the viewport size (that is, the size of the browser's visible area) Element size. In this case, we can specify the height and width of the element using the viewport units vh and vw.

div {
    width: 50vw;
    height: 50vh;
}

In this example, we specify that the width of a div element is 50% of the viewport width and the height is 50% of the viewport height. It should be noted that the viewport unit does not support browsers IE8 and below, so use it with caution.

5. Flexible box layout of CSS3

CSS3 introduces a new feature called flexible box layout (Flexbox), which can more easily implement web page layout and Control of element size. When using Flexbox layout, we can specify the scaling ratio of elements through the flex-grow attribute to easily implement adaptive layout.

.container {
    display: flex;
    flex-direction: row;
    height: 200px;
}

.div1 {
    flex-grow: 1;
}

.div2 {
    flex-grow: 2;
}

In this example, we first set a container element .container and set its display attribute to flex. Then, we specify the height of the container element to be 200 pixels and arrange the child elements in the row direction (i.e. horizontal layout). In the container element, we use two sub-elements .div1 and .div2 and specify their flex-grow properties as 1 and 2 respectively. This means that when there is insufficient horizontal space, .div1 will automatically stretch twice as much to fill the gap.

Conclusion

The above are some common CSS techniques for setting width and height. It is necessary to choose according to actual needs. Reasonable use of these technologies can effectively improve the efficiency and quality of web development. In particular, it is important to note that when laying out a web page, it is very important to choose the appropriate layout method and size settings, which can directly affect the readability and ease of use of the web page, thereby affecting the user experience.

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