I am a WordPress beginner. I want to insert css code into an article but i am getting a too big lines size.

I wrote this in wordpress :
[sourcecode language="css"]
#button{
font-weight: bold;
border: 2px solid #fff;
}
[/sourcecode]
I want something like this :

WordPress’s source code generator uses tables for its layout, so if you have any CSS that affects arbitrary table elements then it will affect the layout of your source code too.