Changing Styles Dynamically

element.style.setProperty('background-color', 'blue', 'important');

Using setProperty with three parameters
The setProperty method accepts a third parameter 'important' to set a CSS property with !important priority. This is the proper way to set important declarations programmatically, rather than concatenating '!important' to the value string. This method ensures proper parsing and handling of the important flag by the browser's CSS engine.
Adding !important to the value string
Using an importance flag
Setting the priority property