UPDATE:This is the better and new version.You can see the old version here

  • Go to the layout section of your blog
  • Go to the edit HTML section and find the b:skin tag.It will be like this]]>(b:ski...)(... denotes n!)change the brackets from() to <>
  • Now paste this code directly above this tag

{
background:#efefef;
border:1px solid #A6B0BF;
font-size:120%;
line-height:100%;
overflow:auto;
padding:10px;
color:#000000 }
pre:hover {
border:1px solid #efefef;
}
code {
font-size:120%;
text-align:center;
margin:0;padding:0;
color: #000000;}
.clear { clear:both;
overflow:hidden;
}


Now type each HTML, Javascript or CSS within (pre) and (/pre)[change brackets for pre from () to <>!]