Follow step by step below
1. Login To blogger dashboard
2. Click "Design" Tab
3. Click "Edit Html" Tab
4. Find The code ]]>
5. Copy and paste scrypt below "Before" ]]> code
.underpost{
padding:10px;
margin:10px 0px;
background:#eee;
border:1px solid #ddd;
line-height:1.6em;}
6. Find the code if you have readmore post, select the second codepadding:10px;
margin:10px 0px;
background:#eee;
border:1px solid #ddd;
line-height:1.6em;}
7. Copy and paste code below "after" code
Type your teks what you want here
Note: You can change the baground color and border color
change teks "type your teks what you want here" with your widget or teks
Hopefully helpfull and good luck.........