html - CSS media queries for screen sizes

Question

I am currently trying to design a layout which will be compatible for multiple screen sizes. The screen sizes I am designing for are listed below:

Screen Sizes:

1. 640x480
2. 800x600
3. 1024x768
4. 1280x1024 (and larger)

The thing that I'm having trouble with is creating the css3 media queries, so that my layout changes when the window's width gets to one of these widths. Below is an example of the media queries I'm currently using, but it is not working for me, so I'm wondering if someone could help me fix it.

<link rel="stylesheet" type="text/css" media="screen and (max-width: 700px)" href="css/devices/screen/layout-modify1.css">
<link rel="stylesheet" type="text/css" media="screen and (min-width: 701px) and (max-width: 900px)" href="css/devices/screen/layout-modify2.css">
<link rel="stylesheet" type="text/css" media="screen and (max-width: 901px)" href="css/devices/screen/layout-modify3.css">

I tried going with a new set of media queries, but they still aren't working for me. Could someone please help explain what I'm dong wrong. Several of you have already tried explaining, but I'm not getting it. The new media queries are displayed below:

<link rel="stylesheet" type="text/css" media="screen and (max-width: 640px)" href="css/devices/screen/layout-modify1.css">

    <link rel="stylesheet" type="text/css" media="screen and (max-width: 800px)" href="css/devices/screen/layout-modify2.css">

    <link rel="stylesheet" type="text/css" media="screen and (max-width: 1024px)" href="css/devices/screen/layout-modify3.css">

    <link rel="stylesheet" type="text/css" media="screen and (max-width: 1280px)" href="css/devices/screen/layout-modify4.css">

Answer 1

Put it all in one document and use this:

/* 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 */
}

/* Desktops and laptops ----------- */
@media only screen 
and (min-width : 1224px) {
  /* Styles */
}

/* Large screens ----------- */
@media only screen 
and (min-width : 1824px) {
  /* Styles */
}

/* iPhone 4 - 5s ----------- */
@media
only screen and (-webkit-min-device-pixel-ratio : 1.5),
only screen and (min-device-pixel-ratio : 1.5) {
  /* Styles */
}

/* iPhone 6 ----------- */
@media
only screen and (max-device-width: 667px) 
only screen and (-webkit-device-pixel-ratio: 2) {
  /* Styles */
}

/* iPhone 6+ ----------- */
@media
only screen and (min-device-width : 414px) 
only screen and (-webkit-device-pixel-ratio: 3) {
  /*** You've spent way too much on a phone ***/
}

/* Samsung Galaxy S7 Edge ----------- */
@media only screen
and (-webkit-min-device-pixel-ratio: 3),
and (min-resolution: 192dpi)and (max-width:640px) {
 /* Styles */
}

Source: http://css-tricks.com/snippets/css/media-queries-for-standard-devices/

At this point, I would definitely consider using em values instead of pixels. For more information, check this post: https://zellwk.com/blog/media-query-units/.