How to make style fixed width:
Open twilightBB/theme/stylesheet.css and find:

CODE: SELECT ALL

#container {
   height: 100%;
   background: #1C1C1C;
   width: 97%;
   text-align: left;
   border: 0;
   padding: 0;
   margin: 0 auto;
   min-width: 900px;
}


Remove min-width: 900px;, and replace width: 96%; with the values of your choice.