bootstrap(響應式)加減輸入框

< div  class = "row" >

  < div  class = "col-lg-6" >

    < div  class = "input-group" >

      < span  class = "input-group-btn" >

        < button  class = "btn btn-default"  type = "button" >-</ button >

      </ span >

      < input  type = "text"  class = "form-control"  placeholder = "2" >

      < span  class = "input-group-btn" >

        < button  class = "btn btn-default"  type = "button" >+</ button >

      </ span >

    </ div >


  </ div >


</ div >