Edit and View Form - Modify width for specific fields

Hi again,

I'm trying to change the default width of some fields in the Edit and View Forms.

What I already got is to modify the width of text fields with this code:

<style>
 .ms-long
   {
     Width: 500px !important;
   }</style>

But now I need to modify the width of the "predecessors" input field...
I know that the width info is here:

<select title="Vorgänger mögliche Werte" id="Predecessors_c3a92d97-2b77-4a25-9698-3ab54874bc6f_SelectCandidate" style="width: 143px; height: 125px; overflow: scroll;" multiple="multiple">

How can I adress that specific width here which is set to 143px?

Thanks in advance!