How to change CSS using jQuery?

Ignore the people that are suggesting that the property name is the issue. The jQuery API documentation explicitly states that either notation is acceptable: http://api.jquery.com/css/

The actual problem is that you are missing a closing curly brace on this line:

$("#myParagraph").css({"backgroundColor":"black","color":"white");

Change it to this:

$("#myParagraph").css({"backgroundColor": "black", "color": "white"});

Here’s a working demo: http://jsfiddle.net/YPYz8/

$(init);
    
function init() {
    $("h1").css("backgroundColor", "yellow");
    $("#myParagraph").css({ "backgroundColor": "black", "color": "white" });
    $(".bordered").css("border", "1px solid black");
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
<div class="bordered">
    <h1>Header</h1>
    <p id="myParagraph">This is some paragraph text</p>
</div>