Long gone are the days when you can expect that your website's visitors will be using a personal computer with Internet Explorer. The increase of Apple's market share, along with the advent of smartphones and tablet computers, has changed the way users access your website. If you haven't changed the way your website works, you may be losing visitors and your business losing money because of your antiquated design. Responsive Web design ensures that your website look its best, no matter the device or browser that your visitor users. This design uses principles of fluidity, media queries and Cascading Style Sheets, or CSS.