It’s a quick little solution to customise the browser’s Address-bar colour as per your website’s theme colour.
By-default the address appears with default colour theme depending upon whether you enabled Dark-mode or not. As it has white colour as default for Google Chrome.
If you have noticed websites like Facebook and more, you can see their Address bar and header looks seamless have same colour shown below.
So, how to achieve this for your website ? Add this one line of code to every page of your website, or if you have a single header file inside any CMS, move towards the file containing all the <head> tag related code and insert the below code snippet there.
<meta name="theme-color" content="#c21f3e">