Why my custom plugin look and feel is different when it is installed as a intellij plugin after jar creation than the one while running as run ide task in intellij

my plugin which i have created runs perfectly fine with the projejct structure of open jdk 8 as the run time version and when i convert it as a jar and install from disk in the plugins settings and restart intellij the look and feel is different. The plugins was created using swings UI and hence when i install as a plugin and use it ,the UI changes and the buttons vanish