the site is moving slightly right or left on clicking between some menu items

You should give some thought to making the site responsive for people on smaller devices.  

1. This is because the content of the resultant page does not create a vertical scrollbar like the other pages do. See here for more: https://css-tricks.com/eliminate-jumps-in-horizontal-centering-by-forcing-a-scroll-bar/

2. This is because of opacity set to 0.7. Change this to a value of 1 and all is well.

.container {
	width: 990px;
	background-color: #FFF;
	margin: 0 auto; /* the auto value on the sides, coupled with the width, centers the layout */
	border-style:;
	border-width:;
	opacity:0.7;
}