I challenged a boss(obviously at a beast temple) and won.  However, the battle isn't closing, and if I try to click the close button I'll lose.

Battle windows do not auto-close to give the players a possbility to study the log.

You already have a log entry that you won, so you won't lose. Closing window results in loss only if the battle is not finished, and you will get a confirmation popup before this.

I see that the right part of battle window is cropped. Close button is located at the right top corner of battle window and isn't visible on the screenshot because of this. You can refresh the browser to get rid of the battle window if you can't zoom out to see the whole layout.

Please say if this is not the case and give us some more details about your problem.

I meant, that I tried clicking the button and it said if I close the window I'll lose, but the problem seems to have fixed itself.:)