Changing a websites background color based on client side (viewers) time is easily done with a small amount of vanilla Javascript.

Changing a website background color or other styles has its uses such as displaying a night mode theme or setting a mode to the users/viewers time.

The only HTML needed is the text to display the time and name for the time (morning, day, evening or night).

Next get the viewers date/time and then format it to only have the hour in 24 hour format

var now = new Date();
var hours = now.getHours();

Build the time string (11:41 AM etc)

var ft = now.toLocaleString("en-US", {
        hour: "numeric",
        minute: "numeric",
        hour12: true
});

Then run if statements to find what style and describer word to use for the given time

if (5 <= hours && hours < 8) {//Morning
        document.write('');//Gradient styled background with white text
        var type = "Morning";//Time describer word
}

Lastly setting the inner HTML of the id ‘time’

document.getElementById("time").innerHTML = `The time is ${ft} it is ${type}`;//The time is 5:18 PM it is Evening

Full code is: