Whether you should master CSS or move to Bootstrap depends on your specific needs and goals.

Mastering CSS:

Advantages:

1. Understanding CSS fully gives you complete control over the styling and layout of your web pages.
2. It allows for greater customization and flexibility in design.
3. You'll have a deeper understanding of how web styling works, which can be beneficial for troubleshooting and optimizing performance.

Considerations:

1. Learning CSS thoroughly can take time and effort.
2. It requires keeping up with updates and new features in CSS.
3. You'll need to write more code compared to using frameworks like Bootstrap.

Using Bootstrap:

Advantages

1. Bootstrap provides pre-designed CSS components and utilities that can speed up development.
2. It offers a responsive grid system, making it easier to create layouts that work well across different screen sizes.
3. It comes with built-in styles for various elements, reducing the need to write custom CSS.

Considerations:

1. Bootstrap has its own learning curve, although it's generally quicker to pick up than mastering CSS from scratch.
2. Your designs may look similar to other websites using Bootstrap if you stick solely to its default styles.
3. Customization beyond Bootstrap's defaults might require additional CSS or overriding existing styles.
4. Consider the following factors to make your decision:
5. Project Requirements: If your project demands unique design or extensive customization, learning CSS fully might be more suitable. For quick prototyping or projects with less emphasis on design customization, Bootstrap can be efficient.
6. Time Constraints: If you need to deliver a project quickly, Bootstrap can save time due to its pre-built components and responsive grid system. Learning CSS fully will take more time initially, but it can offer long-term benefits in terms of flexibility and customization.
7. Long-Term Goals: If you're pursuing a career in web development, understanding CSS thoroughly will be valuable in the long run. However, familiarity with Bootstrap is also beneficial since it's widely used in the industry.

Ultimately, a combination of both skills is ideal. Start with Bootstrap to get projects done efficiently, and gradually deepen your understanding of CSS to enhance your capabilities as a web developer.