Responsive Web Design is nowadays very important. The more customization you need, the more impact it can have on tablets and mobile devices. CSS @media rule
comes in handy here. Three the most popular are:
The declaration below, would work for mobile devices with screen sizes smaller than 768px.
2nd declaration, would work for tablets and other devices like small laptops with screen sizes larger than 768px but less than 1240px.
The last one, would be for desktop devices that has screen width larger than 1240px.
Above @media declarations are only examples that most of you use, so please notice that you are not limited with them only but may define your own instead.