To recap where we left off our exploration of Cascading Style Sheets last week: CSS styles are defined externally from the file they are applied to, internally as a block of style definitions, or in-line as part of individual content elements. And CSS rules are defined for HTML selectors; for classes, which are references in tags that make the tags part of a group that can be collectively modified; and for IDs, which are like tags but are supposed to reference a single tag. All types of style definitions and rules can be used individually or simultaneously.
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