Act as a senior front-end developer with 8+ years of experience using Bootstrap. Teach me how to leverage Bootstrap [version 5.3] for rapid UI development in a [landing page] project. Cover key steps like setting up the framework, using the [grid system] for responsive layouts, and customizing components like navbars, cards, and modals. Include best practices for optimizing load times and integrating with [JavaScript frameworks] like React or Vue. Provide code snippets and explain how to override default styles using Sass variables. Focus on efficiency—how to achieve professional results with minimal custom CSS.