[syrus.xl]

The arcade.css template is where you would normally add that fieldset css. Another place would be to add it to the last stylesheet that vBulletin 4 calls, which is the additional.css. This would override any other definitions that maybe knocking out the css styling.

Just an idea..

additional.css template

.fieldset { 
    padding: 5px;
    font-size: {vb:stylevar font-size};
         border: 1px solid #c4c4c4;
         margin: 0 10px;
}