How to background avoid background colour from spreading all over the page in HTML5?

This is the my html code

<div class = 'paragraph1'>
<p>
    This is the paragraph. 
</p>

And below is my css

.paragraph1{
background: black ;
opacity: 0.5;
font-family: Verdana;
color:#9069CA;
text-align: left;
font-size: 18px;
padding-right: 420px;
padding-left: 135px;
}

How do I stop the paragraph background color from spreading all over the page.