customize a h3 with background color

Hi,

I’m trying to add a background on my h3 only on my services page. I’ve added a class in html view to my title , the class is “service-title”
Then I add this css but the problem is it’s the full width that takes the background color and I only want it around the title. What do I miss in my css? I can’t see.. Can you help me?

Thanks

div.avia_textblock .service-title {
background: #C1D540;
background-size: 210px 40px;
background-repeat: no-repeat;
border: 1px solid;
padding: 5px 25px;
margin: 20px 0px;
text-align: center;
}