Use mediaqueries for mobile first design like;
@media only screen and (max-device-width : 320px) {
/* Styles 320px */
.imageContainer{display:none} /*example for image containing element*/
}
For medium screens;
@media only screen and (min-device-width : 321px)
and (max-device-width : 639px) {
/* Styles upto 640px */
.imageContainer{display:none}
}
And For screens higher than 640px;
@media only screen and (min-device-width : 640px) {
/* Styles above 640px */
.imageContainer{
display:block;
}
.imageContainer img{
width:100%; /*gives full width to all images on this viewport*/
height:auto;
}
}
For Retina displays like iPhone4 and iPad etc;
@media
only screen and (-webkit-min-device-pixel-ratio : 1.5),
only screen and (min-device-pixel-ratio : 1.5) {
/* Styles */
}
And yes, Zooming the viewports are maintained by Meta tag included in your head which is:
<meta name="viewport" content="width=device-width; initial-scale=1.0; maximum-scale=1.0; minimum-scale=1.0; user-scalable=no; target-densityDpi=device-dpi" />