CSS guidance

HTML & CSS
1

How to do following for my web page ?

  1. Increase post area width.
  2. align header image to center
  3. enclose my whole post in a border.
    My site is on wordpress
2

Theme is twenty eleven.

3
  1. #wrapper{width:bigger;}
  2. #header{text-align:center;}
  3. #wrapper #post {border:1px solid;}
    Wordpress: oh forget it I don’t know.
4

there is no wrapper in twenty eleven

5

There seems to be a page wrapper here:


.one-column #page {
    max-width: 690px;
}

Adjust that width if you want it wider.