How change content value of pseudo :before element by Javascript

Question

I have the grap constructured by CSS, which is dynamically changes by JS. I show graph max value by pseudo element as:

.graph:before {
    content:\"\"; //va         


        

Answer 1

You can use CSS variable

:root {
  --h: 100px;
}

.elem:after {
  top: var(--h);
}

let y = 10;

document.documentElement.style.setProperty('--h', y + 'px')

https://codepen.io/Gorbulin/pen/odVQVL