How to apply the information from the input to the element?

Question

css

Hello!
I want to make a text size switch on my site, that is, there will be an input, you select the text size in it and it is applied to certain text on the site, to blocks. Or is the color acceptable, where to dig? Without reloading the page of course.

Answer 1

You can try to set the default font-size to the body, then change it with the input. And for the necessary elements, set the size in rem or em

Answer 2

On js, for example: https://jsfiddle.net/7xae1w13/
Ajax if you need to save without reloading.

Answer 3

Ta-dam
So? Or even tougher?
Like this'c.