Bootstrap form helper - select

Question

I am using select function of Bootstrap form helper now as below fig. show: But I can't change the height or color (use my own color like: #fbc360) I am searching for a while already, but there are no solution workable for my case.

My code as show as below, please someone MONSTER can help me to solve this problem.

<div class="row setup-content step  hiddenStepInfo CreateExp_Step3_FeatureandOreder" id="step-2">
        <div class="col-md-2 left-empty">
        </div><!--Close for left-empty-->
        <div class="col-md-4"  style="padding-right:1vw">
         <div class="CreateExp_periodandorder text-left">
             <h3>
                 Which option would you like pick? <span><small></small></span>
                </h3>
     <div class="bfh-selectbox CreateExp_period" data-name="selectExpTime" data-value="6" value="" >
        <div data-value="1">A</div>
        <div data-value="2">B</div>
        <div data-value="3">C</div>
        <div data-value="4">D</div>
        <div data-value="5">E</div>
        <div data-value="6">F</div>
        <div data-value="7">G</div>
        <div data-value="8">H</div>
        <div data-value="9">I</div>
        <div data-value="10">J</div>
        <div data-value="11">K</div>
        <div data-value="12">L</div>
        <div data-value="13">M</div>
        <div data-value="14">N</div>
        <div data-value="15">O</div>
        </div>                
                
        
                
                
              <div class="NextPreviousPage">
               <hr>
          <div class="col-md-6  text-left">   
                 <p class="btn"  onclick="javascript: resetActive(event, 25, 'step-1');">
                  ← Goback
                 </p>
             </div>
             <div class="col-md-6">
              <div class="btn btn-danger next-step" onclick="javascript: resetActive(event, 50, 'step-3');">
                    Next Page
                 </div>
             </div>
              </div>  
        </div><!--Close for col-md-4-->
        <div class="col-md-3 rightSide-message">
         TBD
        </div>
        <div class="col-md-3 right-empty">
        </div><!--Close for right-empty-->
    </div><!--Close for setup-content-->