HTML commands identify blocks of text as logical entities - paragraphs, headings, list items, etc. HTML has few physical formatting commands. Actual display of a document is determined by the browser's definitions on how a particular type of entity should be handled.
Different browsers display entities different ways, depending on their abilities.
Style sheets give you more control of how entities are displayed. Practical Recommendations Familiarize yourself with the specifications for the HTML tags you use. Think in terms of logically identifying blocks of text, rather than of controlling the appearance of the text.