Gap at top of page despite margin:0 and padding: 0

Question

There's a 32px gap at the top of my site, despite setting margins and paddings to 0. I know it's 32px because I can fix it with padding: -32px. But then I have a gap at the bottom! In Firebug, it seems the body only start 32px down from the beginning of the HTML element, even though I've set margins and paddings to 0.

Here's my CSS:

html {
  height: 100%;
  padding: 0;
  margin: 0;
}

body { 
  background-color: #a7a9ac; 
  color #666666;
  background-image: url('body-bg.gif');
  background-repeat: repeat-x;
  height: 100%;
  padding: 0;
  margin: 0;
}

body, p, ol, ul, td {
  font-family: verdana, arial, helvetica, sans-serif;
  font-size:   13px;
  line-height: 18px;
}

.container_banner h1{
  font-size: 48px;
  position: relative;
  top: 130px;
  left: 250px;
  width: 400px;
}

.container_banner h3{
  position: relative;
  top: 0px;
  left: 32px;
  font-size: 10px;
  color: #F8F8F8;
}

.container_banner{
  position: relative;
  top: 0px;
  background-image: url('banner.png');
  background-repeat: no-repeat;
  margin: 0 auto;
  width: 945px;
  height: 188px;
  padding: 0px;
  background-color: #ffffff;
}

.container{
  position: relative;
  top: 0px;
  margin: 0 auto;
  min-height: 100%;
  width: 945px;
  padding: 0px;
  padding-top: 20px;
  margin-bottom: 0px;
  background-color: #ffffff;
  background-image: url('thin-background.png');
}

.content{
  margin-top: 0px;
  margin-left: 30px;
  min-height: 100%;
}

Container banner is the topmost div, followed by container (which includes content).