Responsive text sizing in Twenty Eleven

Hi Everyone!

I’m using the Twenty Eleven WP theme.

I have a div for a special section with larger font. I’d like this to automatically resize as the browser window shrinks, just like the rest of the text does (mainly the post titles, etc)

Here’s my CSS:

.video_callout {
height:150px;
width:90%;
border-top:1px solid;
border-bottom:1px solid;
border-color: #d1d1d1;
margin-left:auto;
margin-right:auto;
margin-top:5%;
}
.callout_text {
width:50%;
float:left;
text-align:center;
margin-top:2.5%;
}
.callout_image {
width:50%;
float:right;
text-align:center;
margin-top:2.5%
}
.callout_text span.label {
font-style:italic;
font-size:35px;
color:#393939;
}
.callout_text span.duration {
color:red;
font-size:30px;
}

Does anyone know how I can make this specific text responsive?

Thank you!