Media query issues in fluid grid layout (take a look at this code)

Question

how to make adjustments in specific device views without screwing everything up in other views. I know in the css designer when I click global it makes changes to all views which is great. But when I click one of the little icons at the button of the screen (like the smartphone icon or tabet etc) the changes I make in the view dont stay in that view but affect all views. So I'm coming to understand ( maybe wrongly) that those icon have no design power other than to show you what thing look like in that view. I'm starting to focus on clicking the stlye sheet dreamweaver cc created (not the boilerplate one) clicking the media query for the screen size I want to adjust and finding the selector I want to tweek (ITS RIGHT HERE THE HICKUP I'M HAVING IS AT - i CANT ADJUST  IMAGES THAT I HAVE SPECIFICALLY IN THE CORRESPONDING VIEW WITHOUT SCREWING EVERYTHING EVERYWHERE UP IN THE OTHER VIEWS) Can anybody invision what I'm trying to do and what happening and give me a fix????
Idealy I would like to simply click the view icon of the screen size I want to tweak and drag handle bars to resize images and the adjustment stay only in that sceen size range, but this is not happening. This why I say that those (may wrongly I might be doing something wrong) icons have no design power other than to give you a view of things. But either way whether I can click icons and rag handle handle bars or in I have to use css designer I cant specifically work in one view without affecting all the others.
Below is css code for media queries that are in my style sheet. It might not be the cleanest bit I want you to focus on two main aspsects of the code
     1) The media queries, particularly the smartphone 480 and below. ( but all media queries if need be)
     2) In the header and in the list iteams I have images. Its these images that I'm trying to resize - but only specific changes in specific views
Take a look:
/* Mobile Layout: 480px and below. */
.gridContainer {
          margin-left: auto;
          margin-right: auto;
          width: 100%;
          padding-left: 0;
          padding-right: 0;
          clear: none;
          float: none;
#div1 {
#mainheader {
          margin-left: 0;
          position: static;
          height: auto;
          width: 100%;
#navbarone {
#navbartwo {
#listiteams {
          color: #FFFFFF;
          text-align: center;
          background-color: #9DC5D3;
#listiteamstwo {
          text-align: center;
          background-color: #9DC5D3;
          color: #FFFFFF;
#navbutton {
width: 100%;
#li1 {
width: 100%;
clear: both;
margin-left: 0;
#li2 {
width: 100%;
clear: both;
margin-left: 0;
#navbuttontwo {
width: 100%;
#li3 {
width: 100%;
clear: both;
margin-left: 0;
#li4 {
          width: 100%;
          clear: both;
          margin-left: 0;
#flads {
.zeroMargin_mobile {
margin-left: 0;
.hide_mobile {
display: none;
/* Tablet Layout: 481px to 768px. Inherits styles from: Mobile Layout. */
@media only screen and (min-width: 481px) {
.gridContainer {
          width: 100%;
          padding-left: 0;
          padding-right: 0;
          clear: none;
          float: none;
          margin-left: auto;
#div1 {
#mainheader {
          position: static;
          height: auto;
          width: 100%;
          margin-left: 0;
#navbarone {
#navbartwo {
#listiteams {
#listiteamstwo {
#navbutton {
width: 32.2033%;
#li1 {
width: 32.2033%;
clear: none;
margin-left: 0;
#li2 {
width: 32.2033%;
clear: none;
margin-left: 0;
#navbuttontwo {
width: 32.2033%;
#li3 {
width: 32.2033%;
clear: none;
margin-left: 0;
#li4 {
width: 32.2033%;
clear: none;
margin-left: 0;
#flads {
.hide_tablet {
display: none;
.zeroMargin_tablet {
margin-left: 0;
/* Desktop Layout: 769px to a max of 1232px.  Inherits styles from: Mobile Layout and Tablet Layout. */
@media only screen and (min-width: 769px) {
.gridContainer {
          width: 100%;
          max-width: 2000px;
          padding-left: 0;
          padding-right: 0;
          margin: auto;
          clear: none;
          float: none;
          margin-left: auto;
#div1 {
#mainheader {
          position: static;
          height: auto;
          width: 100%;
          margin-left: 0;
#navbarone {
#navbartwo {
#listiteams {
#listiteamstwo {
#navbutton {
width: 32.7731%;
#li1 {
width: 32.7731%;
margin-left: 0;
clear: none;
#li2 {
width: 32.7731%;
margin-left: 0;
clear: none;
#navbuttontwo {
width: 32.7731%;
#li3 {
width: 32.7731%;
margin-left: 0;
clear: none;
#li4 {
width: 32.7731%;
margin-left: 0;
clear: none;
#flags {
.zeroMargin_desktop {
margin-left: 0;
.hide_desktop {
display: none;

Answer 1

By default, image height and width are 100% in FluidGrid Layouts.  You'll find it near the top of your CSS code.
@charset "utf-8";
img, object, embed, video {
max-width: 100%;
.ie6 img {
width:100%;
That's so they can re-scale to fit the various layouts.  If you need to assign explicit height & width values to certain elements, you can override that CSS rule by using the height & width attributes in your HTML code like this. 
<img src="some_image.jpg" height="xxx"  width="xxx">
Or, you can give your image a class name and target that class with CSS Media Queries.  For an example, copy & paste this code into a new, blank document.  SaveAs test.hml and preview in browsers at different screen widths.
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
<style>
/**FLUID GRID DEFAULT**/
img, object, embed, video{
max-width: 100%;
.ie6 img {
width:100%;
/* Special Rules for mobiles */
@media only screen and (max-width: 480px) {
.nav {width:320px; height:74px; }
/* Special Rules for Tablets */
@media only screen and (min-width: 482px) and (max-width: 1024px) {
.nav {width: 480px; height: 148px;}
/* Special Rules for Desktops */
@media only screen and (min-width: 1025px) and (max-width: 1230px) {
.nav {width: 1000px; height: 225px;}
</style>
</head>
<body>
<h3>This image naturally rescales to layout</h3>
<img src="http://placehold.it/1000x225" alt="some description">
<h3>This image has a .nav class &amp; rescales to set media query break points.</h3>
<img class="nav" src="http://placehold.it/1000x225" alt="some description">
</body>
</html>
Does this make sense now?
Nancy O.