We can add, remove or change CSS property values with JavaScript via an element's style property.
Step 1
Get the element via ID or class.
var element = document.getElementById("ID_Name");
Step 2
Change the CSS property.
element.style.opacity = 1;
element.style.fontFamily = 'sans-serif';
The property name changes (not completely!) when we use JavaScript. So, font-family becomes fontFamily.
