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1、Chapter4Chapter4CSSCSS1/51Objectives•CompareCSSformattingwithHTMLformatting.•Describeandcomparethe3levelsofstylesheets.•Comparedifferenttypesofselectors.•Describetheboxmodel.•Usevariousstyles(styleproperties)tomodifypagecontent.2/51CSSvs.HTML•HTML(p130):

2、=“Arial”>Heading1…•CSS:

Heading1

3、ivenalogicalstructureandsemanticmeaningusingHTML.2.Writestylerulesforhoweachelementshouldideallylook.Eachruletargetstheelementbyname,andthenlistsproperties—suchasfont,color,andsoon—tobeappliedtotheelement.3.Attachthestyletothedocument.5/51LevelsofStyleSheets•HTMLstylesheetsarecall

4、edcascadingstylesheetsbecausetheycanbedefinedatthreedifferentlevelstospecifythestyleofadocument.•Lower-levelstylesheetscanoverridehigher-levelstylesheets,sothestyleofthecontentofatagisdeterminedthroughacascadeofstylesheetapplications.6/51LevelsofStyleSheets•Inline-specifiedforaspe

5、cificoccurrenceofatagandapplyonlytothattag–Thisisfine-grainstyle,whichdefeatsthepurposeofstylesheets-uniformstyle•Document-levelstylesheets-applytothewholedocumentinwhichtheyappear•Externalstylesheets-canbeappliedtoanynumberofdocuments7/51LevelsofStyleSheets•Whenmorethanonestylesh

6、eetappliestoaspecifictaginadocument,thelowestlevelstylesheethasprecedence.•Note:IEimplementationisabitdifferent.Ittakesa“nearestfirst”approach.•Example:Whatcolorisit?(page135)8/51LevelsofStyleSheets•Inlinestylesheetsappearinthetagitself•Document-levelstylesheetsappearintheheadofth

7、edocument•Externalstylesheetsareinseparatefiles,potentiallyonanyserverontheInternet–WrittenastextfileswiththeMIMEtypetext/css–tagisusedtospecifythatthebrowseristofetchanduseanexternalstylesheetfile–