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What is the mobile web? The mobile web refers to access to the world wide web, i.e. the use of browser-based Internet services, from a handheld mobile device, such as a smartphone or a feature phone, connected to a mobile network or other wireless network.
Cascading Style Sheets (CSS) is a style sheet language used for describing the look and formatting of a document written in a markup language, most often used to change the style of web pages written in HTML. CSS is designed primarily to enable the separation of document content from document presentation, including elements such as the layout, colors, and fonts.
Very simply, focal-length is the distance from the lens to the film, when focused on a subject at infinity. In other words, focal length equals image distance for a far subject. To focus on something closer than infinity, the lens is moved farther away from the film or sensor. This is why most lenses get longer when you turn the focusing ring.