How to check the validity of your CSS

Validation is the process of checking something against a rule. When you are a beginner, it is very common that you will commit many mistakes in writing your CSS rules. How will you make sure whatever you have written is 100% accurate and up to the W3C quality standards?

If you use CSS, your code needs to be correct. The improper code may cause unexpected results in how your page looks or functions. A CSS validator checks your Cascading Style Sheets to make sure that they comply with the CSS standards set by the W3C Consortium.

Why Validate CSS?

CSS validation helps you −

• Identify syntax errors and typos in your code
• Ensure cross-browser compatibility
• Follow web standards and best practices
• Improve website performance and accessibility

W3C CSS Validation Service

The W3C provides an official CSS validation service that checks your CSS code against current standards. You can validate CSS in three ways −

Method 1: Validate by URL

Enter the URL of your webpage to validate the CSS linked to that page −

Visit W3C CSS Validation Service and enter your website URL in the "Validate by URI" tab.

Method 2: Validate by File Upload

Upload your CSS file directly to the validator −

Use the "Validate by file upload" tab to select and upload your .css file from your computer.

Method 3: Validate by Direct Input

Copy and paste your CSS code directly into the validator −

/* Example CSS to validate */
body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 20px;
    background-color: #f4f4f4;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    background-color: white;
    padding: 30px;
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

HTML Validation First

Before validating CSS embedded in an HTML document, you should first ensure that your HTML is valid. Use the W3C HTML Validator to check your HTML structure.

Common CSS Validation Errors

Conclusion

CSS validation is essential for writing clean, standards-compliant code. Use the W3C CSS Validator regularly during development to catch errors early and ensure your stylesheets work consistently across all browsers.