sun1 : contents and style （内容和格式）
sun2 : syntax and word （句法和词法）
外部样式表
<!--link tag--> <head> <link rel = "stylesheet" type = "text/css" href = "mystyle.css"> </head>内部样式表
<!--css selector--> <head> <style type = "text/css"> body {background-color : red} p {margin-left : 20px} </style> </head>内联样式
<!--style attribute--> <html> <body> <p style = "color : red; margin-left : 20px;"> this is a paragraph </p> </body> </html>
html关键词：tag | element | attribute | value
<start-tag> element contents </end-tag> <!--没有分隔符号--> <start-tag attribute1 = "value1; value1.1; value1.2" attribute2 = "value2" ...... attributeN = "valueN" > element contents </end-tag>css关键词： selector | declaration | property | value
selector {declaration1 ; declaration2 ; ......; declarationN ;} selector { property1 : value1 ; property2 : value2 ; .......; propertyN : valueN ;}
