Design Responsive

Viewport

Set the viewport:

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

Compare devices

CSS Media query

Mobile First and Breakpoints

/* rulesets */

@media screen and (min-width: 500px) {
  /* rulesets */
}

@media screen and (min-width: 1000px) {
  /* rulesets */
}

menu/index.html:

ul {
  display: flex;
  flex-direction: column;
  align-items: stretch;
}

@media screen and (min-width: 700px) {
  ul {
    flex-direction: row;
    justify-content: space-around;
  }
}

@media screen and (min-width: 1000px) {
  ul {
    justify-content: flex-end;
  }
}

Responsive Image

image-responsive/index.html:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  <picture>
    <source media="print" srcset="img/ifpb-hd.jpg">
    <source media="(max-width: 400px)" srcset="img/ifpb.jpg">
    <source media="(max-width: 800px)" srcset="img/ifpb-2x.jpg">
    <source media="(max-width: 1200px)" srcset="img/ifpb-4x.jpg">
    <img src="img/ifpb-hd.jpg" alt="Imagem IFPB">
  </picture>
</body>
</html>

Demo

References