Cascading Style Sheets (CSS) allow separation of document content from document presentation, including elements like fonts, sizes, colors and positioning. There are three main ways to apply CSS rules: inline within HTML tags; embedded within <style> tags in the <head>; or in an external .css file linked via <link>. CSS rules contain selectors that target elements, and declarations that set property-value pairs to style them, such as font-size: 12px. CSS provides control over various text properties including font, size, style, alignment, spacing, decoration and transformation.