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DZone’s Core CSS: Part I is a free, beginner-oriented introduction to CSS fundamentals: separating presentation from markup, writing rules, understanding inheritance, and resolving competing declarations. Molly Holzschlag’s Refcard #019 dates to June 2008, so use it to learn the basic ideas—not as a current guide to CSS specifications or browser support.
What the DZone refcard covers
The refcard is the first installment in a three-part Core CSS series. Its central idea remains useful: keep a document’s content and structure in HTML, and describe its visual presentation with CSS. A shared stylesheet can apply consistent design rules across multiple pages and make coordinated changes easier to maintain.
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The card also introduces selectors, declarations, inheritance, stylesheet placement, the cascade, and specificity. It is available as a free PDF from DZone’s Core CSS: Part I page.
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A CSS rule pairs a selector with a declaration block. The selector identifies the elements to which the declarations apply; each declaration names a property and its value. For example:
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h1 { color: red; }
Here, h1 selects heading elements, while color: red; sets a property-value pair. Holzschlag summarizes the structure this way: “A CSS rule contains at least one selector and at least one declaration within a declaration block.”
What inheritance means
Some CSS properties pass from an element to its descendants when the descendants do not have an applicable value of their own. The refcard uses color as an example: text inside a colored parent can inherit that color. Many box-related properties, including margins and padding, do not work that way by default.
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Inheritance is property-specific, not a general rule that every style flows down the document tree. For a particular property’s current behavior, consult the W3C CSS Cascading and Inheritance Level 5 specification.
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When multiple declarations could apply to an element, the browser resolves them through the cascade. The outcome is not simply “the closest rule wins.” Cascade precedence, selector specificity, and—when competing declarations otherwise tie—source order all matter. The modern cascade also accounts for factors beyond selector specificity, so specificity alone is not a complete explanation.
Specificity is a way of comparing selectors when the cascade calls for that comparison. For a practical explanation and examples, see MDN’s specificity guide. The full modern framework is described in the W3C specification. The refcard’s treatment of !important is a simplified introduction rather than a complete account of modern cascade precedence.
Where styles can be written
The refcard distinguishes browser, user, and author styles, and introduces three common ways authors can provide CSS:
- Inline: a style declaration attached directly to an HTML element.
- Embedded: CSS placed in a document’s style block.
- Linked: CSS kept in a separate stylesheet and connected to the document.
Holzschlag favors linked stylesheets for reuse and maintenance, and cautions against depending on inline and embedded styles in larger professional projects. That is useful introductory advice, not a rule that every modern project must follow; the right approach depends on a project’s architecture and needs.
How to use this 2008 resource today
Read the PDF for foundational concepts, then verify details that depend on current standards or browser behavior. Its discussion of CSS versions—including CSS 1, CSS 2.0, CSS 2.1, and the modular CSS 3 era—reflects the publication period, not a current status report. The same is true of its account of browser inconsistencies, hacks, and workarounds.
For a concise learning path, follow the concepts in this order:
- Understand the separation of HTML structure and CSS presentation.
- Read a rule as selector plus declaration block, then identify each property and value.
- Learn which properties inherit rather than assuming all properties do.
- When styles conflict, use current cascade and specificity references rather than relying on the refcard’s shortcuts.
The refcard is best treated as a historical primer that still introduces durable fundamentals. For current cascade behavior, pair it with the W3C specification and MDN’s specificity guide.
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