Responsive Web Design (ok)

https://www.developer.com/ws/creating-a-mobile-friendly-website.html

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

You can, of course, remove some of the queries, depending on your needs. After deciding which sizes you will customize, you need to decide how the mobile device design should look, i.e. which elements will be removed and which ones will be resized. Then create CSS styles and apply them for each mobile view. Add the following meta tag in the head of your HTML code:

<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" />

Keep in mind that the following meta tag may sometimes cause problems with iPad, so if the design doesn't look good on an iPad, just remove this tag.