Determine whether the element exists or not, and subsequently apply css to it.

edit

To determine if an element exists in the HTML DOM, you can use JavaScript's in-built method called 'document.querySelector'. This method returns the first element that matches a specified CSS selector(s) in the document or null if no such element exists.

To apply CSS to the element, you can use the returned element object and access its style property to manipulate its CSS styles. For example, to change the background color of the element to red, you can use the following code:

//Check if the element with ID 'myElement' exists in the DOM
const myElement = document.querySelector('#myElement');
if (myElement) {
   //Apply CSS to the element
   myElement.style.backgroundColor = 'red';
}

In the above code, the 'document.querySelector' method searches for an element with the ID 'myElement' in the DOM. If it exists, it assigns the element object to the 'myElement' variable. Then, the code checks if 'myElement' is not null (i.e., if an element with the specified ID exists), and subsequently sets its background color to red using the 'style' property.