Using CSS in SAP UI5

Hi Experts,

I am using css (external ) with ui5 .
The structure of my page is like

Index(view>controller)------>index1--->view>Controller

                  index2--->view>Controller

                  index3--->view>Controller

Now should i create separate css for each index1,2,3... ??

I cannot use same css(link to index) for each because in css i am calling directly the ui5 class say:-

.sapMButton{

width : 90%;

}
so the button properties i want to apply only to the puttons present in the index ...not in index1,2,3
if i use same css page to all the index files it is changing all the buttons present in the all the pages ..
what is the best way to structure the css pages for that??