Cannot adjust the width of content and Sidebar

The width of your theme’s .wrap determine how wide your .content and .sidebar can be. So you’ll need to adjust that, too.

/**
 * .wrap is the container of .content and .sidebar
 * The max-width of .content and .sidebar should not be more than the max-width of .wrap
 */

.wrap {
     max-width: 740px;
}

.content {
    width: 100%;
    max-width: 500px;
}

.sidebar-primary {
    width: 100% !important;
    max-width: 200px !important;
}

Don’t adjust the width, just adjust the max-width.

Also, make sure that the combined max-width of .content and .sidebar not exceed that of the .wrap.

—-

As for making the header stick to the top even when scroll, this will do:

/* Stick site-header to top */
.site-header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;

/* when logged in, adjust the position so that the logged-in admin-bar doesn't hide part of the nav */
body.admin-bar .site-header {
    top: 32px;
}

/* give the site body some room at the top */
body {
    margin-top: 96px;
}

I’m unsure what you want by “resize automatically” though? Reduce the height of the nav when scroll?