how to add css to element in javascript code example

Example 1: add style javascript

// Bad:
element.setAttribute("style", "background-color: red;");
// Good:
element.style.backgroundColor = "red";

Example 2: change style js

// select element from DOM
const el = document.querySelector('.para')
// change css style
el.style.color = 'purple'

Example 3: how to change an element in a different elements code css

/*If the cube is directly inside the container:*/

#container:hover > #cube { background-color: yellow; }

/*If cube is next to (after containers closing tag) the container:*/

#container:hover + #cube { background-color: yellow; }

/*If the cube is somewhere inside the container:*/

#container:hover #cube { background-color: yellow; }

/*If the cube is a sibling of the container:*/

#container:hover ~ #cube { background-color: yellow; }