CSS what is the meaning of this code snippet? UPDATED - css

Question

UPDATE
In my style sheet I have a conflict with these snippets. If I keep this one
<style type="text/css">
::selection{ background-color: #E13300; color: white; }
::moz-selection{ background-color: #E13300; color: white; }
::webkit-selection{ background-color: #E13300; color: white; }
then, the gradient effect of the one below works, but the header banner is displaced towards the right. If I remove that, the header banner positions itself correctly, but the gradient effect of the code below does not work :/
body {
background-image:url('../assets/uploads/miweb/gradient2.png');
background-repeat:repeat-x;
margin: 40px;
font: 13px/20px normal Helvetica, Arial, sans-serif;
color: #4F5155;
width:600px;
height:500px;
margin: 0 auto;
}
a {
UPDATE II
These 3 lines
::selection{ background-color: #E13300; color: white; }
::moz-selection{ background-color: #E13300; color: white; }
::webkit-selection{ background-color: #E13300; color: white; }
have a huge impact on the rest of the page
They make this code:
body {
background-image:url('../assets/uploads/miweb/gradient2.png');
background-repeat:repeat-x;
margin: 40px;
font: 13px/20px normal Helvetica, Arial, sans-serif;
color: #4F5155;
width:600px;
height:500px;
margin: 0 auto;
}
be effective. If I remove those 3 lines, the gradient effect will not take effect and the font letters will not be of that family but the standard times roman. However, the negative effect is, like I said, that it displaces to the right a banner that I have as header
I have one header page, one controller and one view and the style sheet to which I have a link in the View

Answer 1

Like the others have said the code doesn't affect the positioning of the elements. Only way that it can affect the header would be if that piece of code is not treated as css at all. Check if the code is in the correct style tags.

Answer 2

The moz is for Firefox and as stated already its for styling. Are you using IE? as if so Id suggest trying alternate browser as well as IE has issues with the double colon which is for css3(no suprise there). have a look here
as I used this when I first came across these and it described them well.

Answer 3

That code shouldn't affect what you're doing. It is code that will change the background colour and text colour of text when it is selected by the user using their mouse.
Could you give us an example link of this happening with it commented out, please?
EDIT
What is the center: attribute supposed to be doing? It isn't valid CSS...