Improvement to material-ui type definition 
Improvement to material-ui type definition 

case 2. Improvement to existing type definition.

From Material-UI Reference (http://www.material-ui.com/#/customization/themes):
"The lightBaseTheme is the default so you will not need to do anything to use it other than using MuiThemeProvider as described in Usage. [http://www.material-ui.com/#/get-started/usage]"

muiTheme Property should be optional.
syuilo/DefinitelyTyped,slavomirvojacek/adbrain-typescript-definitions,AbraaoAlves/DefinitelyTyped,nainslie/DefinitelyTyped,ashwinr/DefinitelyTyped,alvarorahul/DefinitelyTyped,arma-gast/DefinitelyTyped,johan-gorter/DefinitelyTyped,subash-a/DefinitelyTyped,DzmitryDulko/DefinitelyTyped,xStrom/DefinitelyTyped,chrismbarr/DefinitelyTyped,gandjustas/DefinitelyTyped,scriby/DefinitelyTyped,amanmahajan7/DefinitelyTyped,johan-gorter/DefinitelyTyped,HPFOD/DefinitelyTyped,nainslie/DefinitelyTyped,amir-arad/DefinitelyTyped,pocesar/DefinitelyTyped,syuilo/DefinitelyTyped,newclear/DefinitelyTyped,zuzusik/DefinitelyTyped,benishouga/DefinitelyTyped,danfma/DefinitelyTyped,abner/DefinitelyTyped,borisyankov/DefinitelyTyped,damianog/DefinitelyTyped,florentpoujol/DefinitelyTyped,yuit/DefinitelyTyped,DzmitryDulko/DefinitelyTyped,hellopao/DefinitelyTyped,shlomiassaf/DefinitelyTyped,one-pieces/DefinitelyTyped,abner/DefinitelyTyped,magny/DefinitelyTyped,mattblang/DefinitelyTyped,mcliment/DefinitelyTyped,benliddicott/DefinitelyTyped,chrootsu/DefinitelyTyped,shlomiassaf/DefinitelyTyped,georgemarshall/DefinitelyTyped,jraymakers/DefinitelyTyped,progre/DefinitelyTyped,QuatroCode/DefinitelyTyped,abbasmhd/DefinitelyTyped,ashwinr/DefinitelyTyped,benishouga/DefinitelyTyped,psnider/DefinitelyTyped,AgentME/DefinitelyTyped,florentpoujol/DefinitelyTyped,use-strict/DefinitelyTyped,jimthedev/DefinitelyTyped,arusakov/DefinitelyTyped,smrq/DefinitelyTyped,minodisk/DefinitelyTyped,slavomirvojacek/DefinitelyTyped,gandjustas/DefinitelyTyped,dsebastien/DefinitelyTyped,subash-a/DefinitelyTyped,schmuli/DefinitelyTyped,aciccarello/DefinitelyTyped,Ptival/DefinitelyTyped,arma-gast/DefinitelyTyped,schmuli/DefinitelyTyped,isman-usoh/DefinitelyTyped,alvarorahul/DefinitelyTyped,pocesar/DefinitelyTyped,isman-usoh/DefinitelyTyped,rcchen/DefinitelyTyped,martinduparc/DefinitelyTyped,laurentiustamate94/DefinitelyTyped,dsebastien/DefinitelyTyped,rcchen/DefinitelyTyped,jimthedev/DefinitelyTyped,smrq/DefinitelyTyped,alexdresko/DefinitelyTyped,sledorze/DefinitelyTyped,georgemarshall/DefinitelyTyped,arusakov/DefinitelyTyped,GiedriusGrabauskas/DefinitelyTyped,amanmahajan7/DefinitelyTyped,schmuli/DefinitelyTyped,slavomirvojacek/adbrain-typescript-definitions,xStrom/DefinitelyTyped,pocesar/DefinitelyTyped,jraymakers/DefinitelyTyped,micurs/DefinitelyTyped,YousefED/DefinitelyTyped,Ptival/DefinitelyTyped,YousefED/DefinitelyTyped,rolandzwaga/DefinitelyTyped,QuatroCode/DefinitelyTyped,GiedriusGrabauskas/DefinitelyTyped,psnider/DefinitelyTyped,borisyankov/DefinitelyTyped,benishouga/DefinitelyTyped,nycdotnet/DefinitelyTyped,aciccarello/DefinitelyTyped,sledorze/DefinitelyTyped,progre/DefinitelyTyped,slavomirvojacek/DefinitelyTyped,arusakov/DefinitelyTyped,aciccarello/DefinitelyTyped,zuzusik/DefinitelyTyped,mcrawshaw/DefinitelyTyped,alexdresko/DefinitelyTyped,georgemarshall/DefinitelyTyped,yuit/DefinitelyTyped,hellopao/DefinitelyTyped,AgentME/DefinitelyTyped,markogresak/DefinitelyTyped,mattblang/DefinitelyTyped,Penryn/DefinitelyTyped,zuzusik/DefinitelyTyped,nycdotnet/DefinitelyTyped,abbasmhd/DefinitelyTyped,daptiv/DefinitelyTyped,danfma/DefinitelyTyped,AgentME/DefinitelyTyped,donnut/DefinitelyTyped,donnut/DefinitelyTyped,psnider/DefinitelyTyped,minodisk/DefinitelyTyped,scriby/DefinitelyTyped,rolandzwaga/DefinitelyTyped,mcrawshaw/DefinitelyTyped,martinduparc/DefinitelyTyped,jimthedev/DefinitelyTyped,hellopao/DefinitelyTyped,AgentME/DefinitelyTyped,chrootsu/DefinitelyTyped,paulmorphy/DefinitelyTyped,newclear/DefinitelyTyped,magny/DefinitelyTyped,AbraaoAlves/DefinitelyTyped,gcastre/DefinitelyTyped,Penryn/DefinitelyTyped,martinduparc/DefinitelyTyped,damianog/DefinitelyTyped,georgemarshall/DefinitelyTyped,chrismbarr/DefinitelyTyped,HPFOD/DefinitelyTyped,AbraaoAlves/DefinitelyTyped,paulmorphy/DefinitelyTyped,use-strict/DefinitelyTyped,gcastre/DefinitelyTyped