Modify theme in different Screen Sizes ( Media Queries )

Media queries enable us to create a responsive experience, where specific styles are applied to small screens, large screens and anywhere in between.
The media query syntax allows for the creation of rules that can be applied depending on device characteristics.

In General here are the attributes with the results that they return:

min-width -> Rules applied for any browser width over the value defined in the query.
max-width -> Rules applied for any browser width below the value defined in the query.
min-height -> Rules applied for any browser height over the value defined in the query.
max-height -> Rules applied for any browser height below the value defined in the query.
orientation=portrait -> Rules applied for any browser where the height is greater than or equal to the width.
orientation=landscape -> Rules for any browser where the width is greater than the height.

Media queries to change whatever you want through CSS in different screens:

/* Smartphones (portrait and landscape) ----------- */
@media only screen and (min-device-width : 320px) and (max-device-width : 480px) {
/* Styles */
}
/* Smartphones (landscape) ----------- */
@media only screen and (min-width : 321px) {
/* Styles */
}
/* Smartphones (portrait) ----------- */
@media only screen and (max-width : 320px) {
/* Styles */
}
/* iPads (portrait and landscape) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) {
/* Styles */
}
/* iPads (landscape) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : landscape) {
/* Styles */
}
/* iPads (portrait) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : portrait) {
/* Styles */
}
/* iPad 3 ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : landscape) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : portrait) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}
/* Desktops and laptops ----------- */
@media only screen  and (min-width : 1224px) {
/* Styles */
}
/* Large screens ----------- */
@media only screen  and (min-width : 1824px) {
/* Styles */
}
/* iPhone 4 ----------- */
@media only screen and (min-device-width : 320px) and (max-device-width : 480px) and (orientation : landscape) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}
@media only screen and (min-device-width : 320px) and (max-device-width : 480px) and (orientation : portrait) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}
/* iPhone 5 ----------- */
@media only screen and (min-device-width: 320px) and (max-device-height: 568px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}
@media only screen and (min-device-width: 320px) and (max-device-height: 568px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2) {
/* Styles */
}
/* iPhone 6 ----------- */
@media only screen and (min-device-width: 375px) and (max-device-height: 667px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2) {
/* Styles */
}
@media only screen and (min-device-width: 375px) and (max-device-height: 667px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2) {
/* Styles */
}
/* iPhone 6+ ----------- */
@media only screen and (min-device-width: 414px) and (max-device-height: 736px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2) {
/* Styles */
}
@media only screen and (min-device-width: 414px) and (max-device-height: 736px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2) {
/* Styles */
}
/* Samsung Galaxy S3 ----------- */
@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}
@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2) {
/* Styles */
}
/* Samsung Galaxy S4 ----------- */
@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 3) {
/* Styles */
}
@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 3) {
/* Styles */
}
/* Samsung Galaxy S5 ----------- */
@media only screen and (min-device-width: 360px) and (max-device-height: 640px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 3) {
/* Styles */
}
@media only screen and (min-device-width: 360px) and (max-device-height: 640px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 3) {
/* Styles */
}

Alternative if you just want a specific target size for your site, the “min-width:” is where the style will start to have the effect and the “max-width:” is where it ends.
So you can use the example with your numbers in px. :

/* example ----------- */
@media screen and (min-width: 600px) and (max-width: 900px) { /* Styles */ }

Some general information for widths :

@media (min-width:320px) { /* smartphones, portrait iPhone, portrait 480x320 phones (Android) */ }
@media (min-width:480px) { /* smartphones, Android phones, landscape iPhone */ }
@media (min-width:600px) { /* portrait tablets, portrait iPad, e-readers (Nook/Kindle), landscape 800x480 phones (Android) */ }
@media (min-width:801px) { /* tablet, landscape iPad, lo-res laptops ands desktops */ }
@media (min-width:1025px) { /* big landscape tablets, laptops, and desktops */ }
@media (min-width:1281px) { /* hi-res laptops and desktops */ }