Scoped CSS in Vue.js refers to the ability to limit styles to only apply to elements within a specific component, preventing them from affecting other components or elements on the page. Here are some common issues that may arise when using scoped CSS and how to resolve them:

1. Styles Not Applied: If you're seeing that styles defined in a component's scoped style block are not applied to the HTML elements within that component, there could be one of several reasons. First, ensure that your Vue app is properly configured to use scoped CSS. You can do this by adding scoped attribute to the style tag in your component file:

<style scoped>
  /* Your styles here */
</style>

Next, verify that you're using the correct class names or IDs to target the HTML elements that should be styled. If you've followed best practices for naming your classes and IDs, this shouldn't be an issue. However, if you're working with Vue 3 and are trying to use a global style in a scoped component, you may need to adjust your approach.

2. Specificity Issues: When using scoped CSS, the browser applies styles based on specificity. If multiple selectors have the same level of specificity, only the first selector will be applied. To avoid this issue, consider adding unique class names or IDs to the HTML elements you want styled, and then use those in your component's scoped style block.

3. CSS Preprocessor Conflicts: If you're using a CSS preprocessor (e.g., Sass, Less, or Stylus) with Vue.js, there may be conflicts between the preprocessor and Vue's scoped CSS feature. To resolve this issue, ensure that your CSS preprocessor is compatible with Vue.js's scoped CSS feature and follow its documentation for proper integration.

By following these guidelines, you should be able to address many of the issues related to Vue.js scoped CSS.