Media queries

 https://developer.mozilla.org/en-US/docs/Web/HTML/Element/style

https://www.w3schools.com/tags/tag_meta.asp

https://www.w3schools.com/howto/howto_css_image_responsive.asp

https://www.w3schools.com/cssref/css_selectors.asp

What you have to understand is that all responsive layouts always use css to resize the page.

its all at the end the same.

Media Queries detect the size of the browser and loads in additional css.

OR

Viewport load in css based on the device width

@viewport {
width: device-width;
} 

essentially the easiest way to approach a layout if its simple is to make it fluid/100% width and as you need more customization add media queries like this

@media screen and (min-width: 960px){
your css in here
}

its all css, like loading a different set of css files by detecting browser/browser-size/browser-type/device/ device width.

there are no rules!