Responsive web design is the practice of building a website suitable to work on every device and every screen size, no matter how large or small, mobile or desktop. Responsive web design is focused around providing an intuitive and gratifying experience for everyone. Desktop computer and cell phone users alike all benefit from responsive websites.
One popular technique with using media queries is called mobile first. The mobile first approach includes using styles targeted at smaller viewports as the default styles for a website, then use media queries to add styles as the viewport grows.
Float is a CSS positioning property. To understand its purpose and origin, we can look to print design. In a print layout, images may be set into the page such that text wraps around them as needed. This is commonly and appropriately called “text wrap”. Here is an example of that.
Aside from the simple example of wrapping text around images, floats can be used to create entire web layouts.
SMACSS is more style guide than rigid framework. There is no library within here for you to download or install. There is no git repository for you to clone. SMACSS is a way to examine your design process and as a way to fit those rigid frameworks into a flexible thought process.