CSS media query rules - Easy to understand

css-media-query.md

CSS Media Queries: Best Practices

• Media queries have many features, but min-width is the most practical one, the one you should assume to use most of the time.
• Only use em within media query definitions, never pixels.
• Until there's wider rem support within media query, rem should be avoided in media query definitions as well.
• Assuming mobile is 320px and the body font size is 16px, then the breakpoint indicating mobile width in profile orientation would be 20em (320/16).
• Choose breakpoint values to serve the content, not to serve device deminsions.
• Never use media queries to define styles for the smallest viewport size.
• Use media queries to “enhance” or add or alter styles when the browser has a wider (or taller) viewport.

/* Style for every viewport width. */
.Component {
  background-color: tomato;
  color: black;
}

/* Style for viewports greater than 320px wide. */ 
@media (min-width: 20em) {
  .Component {
    background-color: blue;
  }
}