CSS Styles Not Working: Complete Guide

Styles from a custom.css file may not apply due to problems with selector specificity, CSS file loading order, or errors in the CSS code itself. Even if custom.css loads after de_style.css, more specific selectors in de_style.css or syntax errors can block the application of styles.

Table of Contents

• Main Reasons for Non-Working CSS Styles
• Specificity Issues with Selectors
• Impact of CSS File Loading Order
• Debugging Methods Using DevTools
• Practical Solutions
• Syntax Checking

Main Reasons for Non-Working CSS Styles

Font styles may not apply for several key reasons related to how the CSS cascade works. The most common problems include:

Selector specificity conflicts - even if your custom.css loads later, selectors in de_style.css may be more specific. For example, if de_style.css uses a selector like .container p.font-primary while custom.css simply uses p, the more specific selector from de_style.css will take priority.

CSS syntax errors - a single syntax error in the custom.css file can cause all subsequent styles in that file to not be applied. This is especially important to check when working with complex font rules.

Incorrect HTML structure - if the elements you’re applying styles to have a different structure than expected, the selectors might not find the right elements.

Problems with the CSS cascade often occur precisely because developers underestimate how specificity and loading order interact with each other.

Specificity Issues with Selectors

Specificity is one of the most important aspects of CSS, which determines which styles will be applied when there’s a conflict. If styles from custom.css aren’t working, the problem is almost always related to selector specificity.

Factors affecting specificity:

• ID selectors (highest specificity)
• Class, attribute, and pseudo-class selectors
• Element and pseudo-element selectors (lowest specificity)

As noted in MDN Web Docs, “CSS declarations marked as important override any other declarations within the same cascade layer and origin. Although technically, !important has nothing to do with specificity, it interacts directly with specificity and the cascade.”

To solve specificity issues, you can:

1. Increase the specificity of selectors in custom.css
2. Use more specific selectors
3. Apply !important (but this is considered an anti-pattern)

Example of a problem:

/* In de_style.css */
.container .text { font-family: Arial; }

/* In custom.css */
.text { font-family: 'Times New Roman'; } /* Won't work */

Solution:

/* In custom.css */
.container .text { font-family: 'Times New Roman'; }

Impact of CSS File Loading Order

Loading order of CSS files is indeed important, but only when selector specificity is equal. If you have equal specificity, the last rule in the code takes priority.

According to research from CSS-Tricks, “using the :where pseudo-selector allows us to drop specificity down to ‘after default styles from user-agent’, regardless of when the CSS is loaded in the document.”

If styles from custom.css aren’t being applied despite the file loading later, check:

1. Verify the CSS connection order in HTML:

<!-- CORRECT order -->
<link rel="stylesheet" href="de_style.css">
<link rel="stylesheet" href="custom.css">

2. Check for @import within files:

/* If de_style.css contains: */
@import 'other-styles.css'; /* This can disrupt the order */

3. Ensure there are no overrides in other files

As explained in Stack Overflow, “include your stylesheet last on the page and use higher specificity for your rules”.

Debugging Methods Using DevTools

Browser developer tools are your best friend when debugging CSS styles. Modern browsers provide powerful tools for analyzing cascade and specificity issues.

Step-by-step debugging:

1. Open DevTools (F12 or Ctrl+Shift+I)
2. Select the element with problematic styles
3. Go to the “Styles” or “Computed” panel
4. Review applied styles - those that are crossed out are overridden

As noted by Smashing Magazine, “DevTools manipulate the order in the Styles panel to show the most applicable styles at the top. Then we can see that the color property for just p is crossed out as an additional indicator that this declaration rule isn’t being applied”.

Useful debugging techniques:

• Use the “inspect element” button for quick analysis
• Temporarily disable styles to see the effect
• Check the console for CSS errors
• Use the “Computed” panel to see final values

With these tools, you’ll quickly identify where the problem lies - in specificity, loading order, or syntax errors.

Practical Solutions

A systematic approach to solving CSS style problems will help you effectively fix issues. Here are several practical methods:

1. Checking Selector Specificity

/* Problem */
.title { font-size: 16px; }
.de-style .title { font-size: 14px; } /* Overrides */

/* Solution */
.de-style .page-title { font-size: 16px; } /* More specific selector */

2. Using !important (carefully)

.title {
  font-size: 16px !important; /* Use only in extreme cases */
}

3. Organizing CSS Files

<!-- Recommended order -->
<link rel="stylesheet" href="normalize.css">
<link rel="stylesheet" href="de_style.css">
<link rel="stylesheet" href="custom.css">
<link rel="stylesheet" href="responsive.css">

4. Grouping Related Styles

/* Instead of scattered rules */
.font-primary { font-family: Arial; }
.font-secondary { font-family: Times; }

/* Use an organized approach */
.font-system {
  font-family: Arial, sans-serif;
}
.font-serif {
  font-family: 'Times New Roman', serif;
}

Tip: As recommended by DigitalOcean, “when you work with websites, there’s usually JavaScript that applies inline styles loading. Elements with style attributes are at the bottom of the cascade”.

Syntax Checking

Syntax errors in CSS are one of the most common reasons why styles don’t apply. Even a single typo can cause all subsequent rules in the file to be ignored.

Typical syntax problems:

• Missing dots or hashes before class/ID selectors
• Improper use of brackets and semicolons
• Errors in property values
• Unclosed code blocks

Tools for syntax checking:

1. W3C Validator - https://jigsaw.w3.org/css-validator/
2. IDE Extensions - VS Code, Sublime Text, WebStorm
3. Browser Console - shows syntax errors

Examples of syntax errors:

/* INCORRECT */
.container {
  font-family: Arial; /*缺少分号*/
  color: red
}

/* CORRECT */
.container {
  font-family: Arial;
  color: red;
}

As explained in Stack Overflow, “CSS rules don’t always ‘cascade’ the way you might expect. The priority of CSS rules is known as specificity”.

For complex projects, it’s recommended to use CSS preprocessors (Sass, Less) or CSS-in-JS solutions, which help avoid syntax errors and improve code organization.

Sources

1. Don’t Fight the Cascade, Control It! | CSS-Tricks
2. Specificity - CSS | MDN
3. How To Apply CSS Styles to HTML with Cascade and Specificity | DigitalOcean
4. A Guide To CSS Debugging — Smashing Magazine
5. html - Why is my CSS style not being applied? - Stack Overflow
6. Troubleshooting CSS - Learn web development | MDN

Conclusion

The main reason styles from custom.css don’t apply despite late loading is usually related to selector specificity issues or syntax errors. To solve the problem, you need to:

1. Check selector specificity - ensure that selectors in custom.css are specific enough to override styles from de_style.css
2. Use DevTools - browser tools will help you determine exactly which rules are overriding your styles
3. Check CSS syntax - make sure there are no syntax errors in custom.css
4. Optimize loading order - with equal specificity, the last rule takes priority

To prevent similar problems in the future, it’s recommended to use CSS organization methodologies, check syntax before uploading to the server, and regularly use developer tools for diagnosing issues.