Help with <h3> tags

Can I get rid of the line break?

[Rightz]

Hi,

I've been told using H3 etc tags are better than simply using bold for the serps so I'm trying to change them. However the text is in a box so I don't want a line break under it. Is there anyay to do this?

[Ingolemo]

h3 {
padding:0;
margin:0;
}

[Rightz]

genius thanks