Check out example codes for "css media query responsive sizes". It will help you in understanding the concepts better.

Code Example 1

320px
480px
600px
768px
900px
1024px
1200px

Code Example 2

/* Extra small devices (phones, 600px and down) */
@media only screen and (max-width: 600px) {}

/* Small devices (portrait tablets and large phones, 600px and up) */
@media only screen and (min-width: 600px) {}

/* Medium devices (landscape tablets, 768px and up) */
@media only screen and (min-width: 768px) {}

/* Large devices (laptops/desktops, 992px and up) */
@media only screen and (min-width: 992px) {}

/* Extra large devices (large laptops and desktops, 1200px and up) */
@media only screen and (min-width: 1200px) {}

Code Example 3

/* Mobile first, baby! */
/* Medium devices (landscape tablets, 768px and up) */
@media only screen and (min-width: 768px) {}
/* Large devices (laptops/desktops, 992px and up) */
@media only screen and (min-width: 992px) {}
/* Extra large devices (large laptops and desktops, 1200px and up) */
@media only screen and (min-width: 1200px) {}

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