Removes admin script + wp_enqueue tweaks

It didn't seem worth the additional http headers just for one css property so I changed the style to be inline. I'd say this is fine for a 1 off style tweak but if more styles needed to be added in the future then worth splitting it out into a new file again.

I also expanded the wp_enqueue call to include dependency and a version number. 

Finally I also swapped the span for a label

Thanks Tom!