Table of Contents
Basics of CSS picture size adjustment
Property Selector: Exact Matching and Common Traps
Home Web Front-end HTML Tutorial Solve CSS image size adjustment: Attribute selector and best practices

Solve CSS image size adjustment: Attribute selector and best practices

Aug 25, 2025 pm 10:09 PM

Solve CSS image size adjustment: Attribute selector and best practices

This article explores in-depth common reasons for invalid image size adjustment in CSS, especially when using attribute selectors (such as img[src="..."]), the styles that do not take effect due to mismatch of src attribute values. The article provides detailed sample code, corrects common errors, and recommends the use of more robust class (class) or ID (id) selectors as best practices for style control to improve the maintainability and readability of the code.

Basics of CSS picture size adjustment

In web development, resizing image size is a common requirement. Generally, we can control the display size of the image through the width and height properties of CSS. These properties can be applied directly to the Solve CSS image size adjustment: Attribute selector and best practices tag or specified by selectors (such as element selectors, class selectors, ID selectors, or attribute selectors).

For example, set the width for all images:

 img {
  width: 100%; /* The image width accounts for 100% of the parent container */
  height: auto; /* Automatic height adjustment to maintain image proportion*/
}

Or set a fixed size for a specific picture:

 .my-image {
  width: 250px;
  height: 150px; /* may cause image deformation, usually only one dimension is set */
}

Property Selector: Exact Matching and Common Traps

CSS Attribute Selector is very useful when you need to apply styles based on an attribute value of an HTML element. For example, img[] is a common attribute selector that selects all Solve CSS image size adjustment: Attribute selector and best practices elements whose src attribute values ​​exactly match the specified string.

Problem examples and analysis:

Many developers may encounter the problem that the style does not take effect when using the img[src="..."] selector, even if it seems that the src path is correct. This is usually because the src attribute value has a subtle inconsistency in the CSS selector with the actual value in the HTML code.

Consider the following HTML code:

 <img  src="/static/imghw/default1.png" data-src="https://media.istockphoto.com/photos/colored-powder-explosion-on-black-background-picture-id1140180560?k=20&m=1140180560&s=612x612&w=0&h=X_400OQDFQGqccORnKt2PHYvTZ3dBLeEnCH_hRiUQrY=" class="lazy" alt="Solve CSS image size adjustment: Attribute selector and best practices" >

If you try to resize the image using the following CSS code, you may find that the style does not take effect:

 /* Wrong CSS selector*/
img[src="https://media.istockphoto.com/photos/colored-powder-explosion-on-black-background-picture-id1140180560?k=20&m=1140180560&s=612x612&w=0&h=X_400OQDFQGqccORnKt2PHYvTZ3dBLeEnCH_hRiUQrY"] {
  width: 250px;
}

If you look closely at the src value in the above-mentioned wrong CSS selector, you will find that it is one equal sign = less than the actual src value in HTML. The attribute selector requires that the attribute value must match exactly , including every character. Even one character or one less character will cause the selector to fail to match the target element.

The correct solution:

To solve this problem, just make sure that the src attribute value in the CSS selector is exactly the same as the actual src attribute value in HTML.

 

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