One option is to use float.
advantages: it does not create spaces between elements
disadvantage: elements after the floated buttons will be floated, too, which means you will have to use a clearfix. If this is the last line of your file, then you can use it.
The other is to use inline-block.
advantages: no need for clearfix
disadvantage: spaces between divs.
So, using the latter option:
Notice that I cannot give it 33.3% width because of the spaces between divs. If I were to make width:33.3%, Div3 would drop on the next row. So the html code needs reformatting like this:
With spaces eliminated, I can change the width of the divs to 33.3% and they will remain on the same line.
Let me know if there is something here that is unclear. Paste this code in here and play with it.