Okkkay - so was having a blonde moment!!!

Apparently my site is feeding from classic > css
Not template default > css

I'm off to sit in the corner with my dunce hat on......

This works a treat:
[FONT=Calibri].sideBoxContent {[/FONT]
[FONT=Calibri] background-color: #ffffff;[/FONT]
[FONT=Calibri] padding: 0.4em;[/FONT]
[FONT=Calibri] text-align: left;[/FONT]
[FONT=Calibri] }[/FONT]