学步园

  浏览器本身是设置一些默认的css属性，这个属性的加载位置是在

CSSStyleSelector.cpp

static void loadFullDefaultStyle()
{
    if (simpleDefaultStyleSheet) {
        ASSERT(defaultStyle);
        delete defaultStyle;
        delete simpleDefaultStyleSheet;
        defaultStyle = new CSSRuleSet;
        simpleDefaultStyleSheet = 0;
    } else {
        ASSERT(!defaultStyle);
        defaultStyle = new CSSRuleSet;
        defaultPrintStyle = new CSSRuleSet;
        defaultQuirksStyle = new CSSRuleSet;
    }

    // Strict-mode rules.
    String defaultRules = String(htmlUserAgentStyleSheet, sizeof(htmlUserAgentStyleSheet)) + RenderTheme::defaultTheme()->extraDefaultStyleSheet();
    CSSStyleSheet* defaultSheet = parseUASheet(defaultRules);
    defaultStyle->addRulesFromSheet(defaultSheet, screenEval());
    defaultPrintStyle->addRulesFromSheet(defaultSheet, printEval());

    // Quirks-mode rules.
    String quirksRules = String(quirksUserAgentStyleSheet, sizeof(quirksUserAgentStyleSheet)) + RenderTheme::defaultTheme()->extraQuirksStyleSheet();
    CSSStyleSheet* quirksSheet = parseUASheet(quirksRules);
    defaultQuirksStyle->addRulesFromSheet(quirksSheet, screenEval());

}

红色的部分就是对应的用自动生成工具生成的cpp文件

最终将默认的属性和访问网站的css属性进行混合，比较出优先级，得到最终一张css的渲染列表

最终display到页面上。