php - How big can CMS database be? -

planing build simple cms (with php) own educational needs , ran problem design have never encountered in book or tutorial.
if wanted let used mess around colors example. how do that? idea had make database such options , echo them site normal css. thet mean load db every single time visits webasite. seems me overload website. again, have never encountered such problem. or there way of doing more easily?

thanks every answer!

edit:
create system enables user change css via cms. example background color, drop-down menu colors, text sizes, fonts , lot of other stuff handeled css. simple customization.
asking 2 questions.

1. how? system should use? no book/tutorial read never covered editing css files using php have no idea how that. or maybe there better ways of doing it?
2. i had idea how store customisable data. in database wanted know how big can , whether problem when posibly tens or maybe houndreds of variables loading site.

edit2:
, btw never worked wordpress or other cms , kind of expected options looking present there, true? in mind such feature essential user inexperienced computers. understand link provided sam (http://css-tricks.com/css-variables-with-php/), it's not common. it's quite complicated thing , might harm performance of website.

i hope made question clear now.

i know has tons of downvotes, can cache database queries. can mimic css file using header type in php. see http://css-tricks.com/css-variables-with-php/

this allow browser cache css file generated php & mysql. means database called when cache expires.

in terms of size never reach limit describing.

update

these sort of features bit unorthodox, using cached version of generated css file mandatory.

what can include text editor within cms edit css file, each user can have own css file overrides default 1 if changed. letting them edit directly can change layout themselves. can limit them changing colours / font-sizes etc.