Header size help

[homeslicee]

I want to know the default size of the gradient blue and white bar at the top of the smf forum theme "core" I am using it and want to place a large image the width of the gradient bar but at a height taller what size would it have to be and where would I replace the code to make this work?

[Eudemon]

can you give an example forum that uses "core" theme
im currently using school's computer so i can't test it out

[ARG01]

I never install the core theme but if you have a link to a site that is using it I can help you. 

[Illori]

http://www.simplemachines.org/community/index.php?theme=11

[Eudemon]

the top bar is the same width as mainframe
#mainframe {
    font-size: 85%;
    margin: auto;
    width: 95%;
}
which is a percentage width
if you want it to be a specific size, find this code in your index.css
change 95% to the specific size you want, example 1400px

[homeslicee]

but if i change it to a specific size will that mess up the size of the border of my theme and site, left at 95% will allow it to remain stable? And what is a good size to make the header image, u just said 1400 as an example but what is an actual size I should use, my site is hxxp:www.taybyat.com [nonactive] take a look

[Eudemon]

changing it to a specific size should not mess up your forum
altho percentage is recommended, it's more flexible, leave it as it is if you wish
what good size? it really depends on your visitor's  screen resolution
for example if you make a banner 1400px, the user has a resolution of 1600
1400-1600*0.95=-120px, he will then see your banner + a 120px original background
you can also repeat your background, in that case it would be your banner + 120px part of your banner