Different web browsers behave differently

I guess it is kind of obvious for everyone but one more example does not hurt... I am sure there is some way to make the webpage appear similar but so far I am not sure how. Should I stop worrying about the details and just plow on?

  /* CSS layout */

body {

margin: 10;

padding: 10;

font-family: Verdana, Arial, Helvetica, sans-serif;

font-size: 0.8em;

color: #000;

background-color: silver;

}

#masthead {

background-color: maroon;

margin:2%;

}

#top_nav {

margin: 2%;

background-color: maroon;

}

#container {

min-width: 75%;

}

#left_col {

margin-left: 2%;

width: 18%;

float: left;

}

#page_content {

margin-left: 22%;

margin-right: 2%;

}

#footer {

clear: both;

margin:2%

}