Thanks for your response, and sorry for the late.
There were already a #container in the graphene theme:
#container {
-webkit-box-shadow: 0 0 10px #000;
box-shadow: 0 0 10px #000;
}
So I added the float attribute:
#container {
-webkit-box-shadow: 0 0 10px #000;
box-shadow: 0 0 10px #000;
float left;
}
Result is good, but I would like to let a space between the left border and the theme, do I replace the float attribute by margin left?