Prevent SCSS from changing your CSS class names3 min read

Introduction

Sometimes, when working on a SPFx project, I just want to define a CSS class in my .scss file but I don’t want the SASS pre-processor to append random strings to my class names.

For example, let’s say I wanted to customize the DocumentCard elements within my SPFx web part to add a border. If I write my SCSS like this:

.myWebPart .ms-DocumentCard {
    border: 2px solid red;
}

It won’t work.

That’s because when building my solution, the SASS pre-processor will append random strings to my class names. So, my .myWebPart and .ms-DocumentCard CSS classes might become .myWebPart-223 and .ms-DocumentCard-242.

The problem is, I don’t want my CSS classes to change from .ms-DocumentCard to .ms-DocumentCard-242 because the .ms-DocumentCard CSS class comes from another component (in this case, Microsoft’s Fabric UI DocumentCard).

Luckily, there’s a way around it. Every time I need to remember how to do it though, I find myself having to re-open old projects.

Using the :global pseudo selector

To prevent the SASS pre-processor from appending random strings to my CSS class name, just use the :global pseudo selector.

For example:

:global(.ms-DocumentCard) {
    border: 2px solid red;
}

You should be careful, though: global CSS changes apply, well, globally. This means that if you use global(.ms-DocumentCard) in your CSS, every single element with a CSS class of .ms-DocumentCard on the entire page will be affected — not just the ones in your web part.

If you want to override styles within your web part, use a CSS selector that is a bit more restrictive; something like this:

.yourWebPart {
    :global(.ms-DocumentCard) {
        border: 2px solid red;
    }
}

If you need to define a whole bunch of CSS classes that you don’t want to be renamed, you can define a global block, as follows:

:global {
  .ms-DocumentCard {
    border: 2px solid red;

    .ms-DocumentCard--compact {
      .ms-DocumentCardPreview {
        -ms-flex-negative: 0;
        flex-shrink: 0;
        width: 144px;
      }
    }

    .ms-DocumentCardPreview-icon img {
      width: 32px;
      height: 32px;
    }
  }

  .ms-DocumentCard:not(.ms-DocumentCard--compact) {
    ...
  }
}

More information

When you create a SPFx solution, the Yeoman generator creates a [YourWebPartName].module.scss file automatically for you.

You may have asked yourself why the file isn’t just called [YourWebPartName].scss instead of [YourWebPartName].module.scss. Well, as it turns out, the .module part of the file name is what instructs the pre-processor to make every CSS class names unique.

If you changed your .scss file to [YourWebPartName].scss, the pre-processor would stop renaming the CSS class names, but you’d risk getting more issues; instead of being scoped to your web part, the CSS classes would be globally applied to the page.

Instead, it is better to continue using [YourWebPartName].module.scss and use the :global pseudo selector.

By the way, if you want to define a local CSS class name within a global block, simply use the :local pseudo selector. It works exactly the opposite of the :global pseudo selector.

For example:

:global {
  .ms-DocumentCard {
    border: 2px solid red;

        :local(.myDocument) {
            border: 2px solid green;
        }
    }
}

Conclusion

SCSS rocks, but sometimes it can be annoying how the CSS class names are automatically renamed to make them unique.

To prevent renaming a class name, use :global() or :global { } in your SCSS.

Whatever you do, resist the urge to make all your CSS classes global.

I hope it helps?

Photo Credit

Image by Christoph Meinersmann from Pixabay