CSS optimize, extract common part?

[dudeno]

for the following css style:\[code\]#div a {color:red}#div li {width:100px}#div span {font-size:10px}\[/code\]is there any way to write the rules above to\[code\]#div{a {color:red}li {width:100px}span {font-size:10px}}\[/code\]so just need to write #div once and easy to remove or modular different area of the webpages