using javascript to change csss code example

Example 1: how to change style of an element using javascript

<html>
<body>

<p id="p2">Hello World!</p>

<script>
document.getElementById("p2").style.color = "blue";
</script>

<p>The paragraph above was changed by a script.</p>

</body>
</html>

Example 2: 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; }