1.html5的文档规范是什么?
<!DOCTYPE html>
2.一个div如何控制位于页面的正中间位置
1 <!doctype html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <title>div绝对定位</title> 6 <style> 7 div{ 8 background:url(images/img2.jpg); 9 background-position:center; 10 background-repeat:no-repeat; 11 background-size:500px 200px; 12 width:500px; 13 height:200px; 14 margin:0 auto; 15 } 16 .tcenter{ 17 margin:0 auto; 18 top:0; 19 } 20 .tright{ 21 margin:auto; 22 position:absolute; 23 top:0; 24 right:0 25 } 26 .tleft{ 27 margin:auto; 28 position:absolute; 29 top:0; 30 left:0 31 } 32 .center{ 33 margin:0 auto; 34 position:absolute; 35 top:50%; 36 left:50%; 37 margin-left:-250px; 38 margin-top:-100px; 39 } 40 .bright{ 41 margin:0 atuo; 42 position:absolute; 43 right:0; 44 bottom:0; 45 } 46 .bleft{ 47 margin:0 auto; 48 position:absolute; 49 bottom:0; 50 } 51 .bcer{ 52 margin:0 auto; 53 position:absolute; 54 left:50%; 55 margin-left:-250px; 56 bottom:0; 57 } 58 </style> 59 </head> 60 61 <body> 62 <div class="tcenter">center</div> 63 </body> 64 </html>