Overview

Responsive designs automatically adjust for different screen sizes and viewports:

To achieve responsive design:

• Always set the viewport in the meta tag

Images

• Set the CSS width property to 100% to allow the image to scale up and down
• Set the CSS max-width property to 100% to allow the image to scale down, but never scale up
• Use the <picture> element to use different images for different browser window sizes.

Text

• Set the CSS font-size property with a viewport value (the viewport is the browser window size):

<h1 style="font-size:10vw">Hello World</h1> <!-- 10vw is 10% of the viewport size -->

Media Queries

Use media queries to change layouts based on browser sizes, like this one that changes from a horizontal stack to a vertical stack:

<style>
.left, .right {
    float: left;
    width: 20%; /* The width is 20%, by default */
}

.main {
    float: left;
    width: 60%; /* The width is 60%, by default */
}

/* Use a media query to add a breakpoint at 800px: */
@media screen and (max-width: 800px) {
    .left, .main, .right {
        width: 100%; /* The width is 100%, when the viewport is 800px or smaller */
    }
}
</style>