@mkwan: For your first question, when you reduce the width of your sidebar, you have to keep in mind of responsive screensize. So, I don’t recommend you to change this.
2. to change the color of the menu bar at the top, just add the following CSS in “Custom CSS” box in theme Options panel.
/* Main menu Background color */
#header-menu { background-color: #3a3d41; }
/* For menu active color */
#header-menu .menu .current-menu-item > a,
#header-menu .menu .current-menu-ancestor > a,
#header-menu .menu .current_page_item > a,
#header-menu .menu .current_page_ancestor > a,
#colophon .menu .current-menu-item a {
background-color: #000000;
}
/* For Menu hover color */
#header-menu ul.menu li:hover > a,
#header-menu ul.menu a:focus,
#colophon #access-footer ul.menu a:hover,
#colophon #access-footer ul.menu a:focus {
background-color: #2d2d2d;
}
/* For Sub-menu color */
#header-menu ul.menu ul a {
background-color: #3A3D41;
}