Changed website width with boxed layout but width does not change.

I have a screen 1280px I went into general Layout and changed the width to 1280 and the content and sidbare width at 100% but the width did not change.

I found the following css code.

@media only screen and (min-width: 1140px) {
.responsive .boxed#top {
width: 1280px;
}
}
It changed the header width but not the content width. When I used “inspector” it said the Div containing the content and sidebar was only 1010px

Please advise.