what does this media query mean.

It means that for any device or screen that displays the site at a 312px or over, apply those CSS Style rules to the elements on the page.

you did explain only first line on the code, which i already know what it is.

These are called ‘selectors’ in CSS:

.wrap,
#search-wrapper .searchform

This is one set of selectors:

.wrap

And this is another set of selectors:

#search-wrapper .searchform

Multiple selectors can be changed using a comma.

This style represents a ‘maximum width’:

max-width: 264px;

In this case, the maximum width is 264px.

If that still doesn’t answer your question, can you please rephrase it? The thread title currently asks about what the Media Query means, which you’ve said you already understood. So I’ve explained what the other bits of the code means.

sorry, i though that keyword ” this ” mean details.

so how to know what those selectors do, because i can’t find them inside style.css .

because every media screen have at least :
1: wrap
2:#search-wrapper .searchform
and this one has an
3 #secondary

so where are those classes “if they are ” to know what they mean so i can manipulate them.