Is used to brand the address bar of a website (only on mobile devices) in a selected Hex-color.
<meta name="theme-color" content="#317EFB">
content can be any valid Hex-color or CSS color-value.
There can also be a
media-attribute added to define in which system-color-scheme which color should be used for the address bar:
<meta name="theme-color" content="#317EFB" media="(prefers-color-scheme: dark)">
theme-color is defined in the HTML Specification and is therefore a HTML Standard.
In the WHATWG WikiUp to date: v2.3.3