By the look of your right hand toolbar, you have opened the Styles Tab, it is showing as highlighted’
My guess is you opened it and changed the style.
You can open it again and change the style back to what you want.
If you open that tab then click the small house icon it will show you what styles you have used in your model and you should be able to choose the original.
ok will have a check now to see if that is it be back in 1 minute
Now click the Purge Unused button at the bottom right of the Styles panel.
Ok thank you!