2. User Interface and User Experience (UI/UX)# 2.1. Overview 2.1.1. What is UI/UX? 2.1.2. Why is UI/UX Important? 2.1.3. What Will You Learn in This Module? 2.2. Responsive Web Design 2.2.1. Flexbox and Grids 2.2.2. Detecting the Device Display Size 2.2.3. Adjusting Content Size and Layout 2.2.4. The Viewport Meta Tag 2.3. Front End Frameworks 2.3.1. What Are Front-End Frameworks? 2.3.2. Getting Started 2.3.3. Bootstrap’s Grid System 2.3.4. Responsive Design and Breakpoints 2.3.5. Styling 2.4. CSS Preprocessors 2.4.1. Motivation 2.4.2. Sass 2.4.3. Bootstrap and Sass 2.5. Performance 2.5.1. Why is Performance a UX Issue? 2.5.2. Evaluating Page Performance 2.5.3. Improving Page Load Time