I have written a navigation bar based on the example given in the components link in Bootstrap. But the navigation bar does not collapse in a right way as it is supposed to do. As shown in the process below:
State 1

State 2

State 3

the navigation bar is not collapsed sharply, rather, it will become 2 columns first and then collapse.
I have found a same problem that has been asked previously in stackoverflow. It seems like the problem is caused by the default breaking point defined in bootstrap. However, I do not know where to change the breaking point and how can I do it.
I am using the latest bootstrap version, and following is the snippet of my navigation bar code.
Thanks in advance for any help and advice!
<!--navigation bar-->
    <nav class="navbar navbar-inverse navbar-fixed-top">
        <div class="container">
            <div class="navbar-header"><!--brand and toggle get grouped for better mobile display-->
                <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navItems">
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                </button>
                <a class="navbar-brand" href="#">Logo</a><!--end of logo-->
            </div><!--end of logo & collapsing logic-->
            <div class="collapse navbar-collapse" id="navItems">
                <ul class="nav navbar-nav">
                    <li><a href="#main" class="scroll">HOME</a></li>
                    <li><a href="#about" class="scroll">ABOUT</a></li>
                    <li><a href="#work" class="scroll">WORK</a></li>
                    <li><a href="#blog" class="scroll">BLOG</a></li>
                    <li><a href="#contact" class="scroll">CONTACT</a></li>
                </ul><!--end of menu list-->
                <form class="navbar-form navbar-left">
                    <input type="text" class="form-control" placeholder="Search on this site" id="searchInput ">
                    <button type="submit" class="btn btn-default"><span class="glyphicon glyphicon-search"></button>
                </form><!--end of search bar-->
                <ul class="nav navbar-nav navbar-right">
                    <li class="dropdown">
                        <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false"><span class="glyphicon glyphicon-user"></span> My Account <span class="caret"></span></a>
                        <ul class="dropdown-menu" role="menu">
                            <li><a href="#"><span class="glyphicon glyphicon-wrench"></span> Settings</a></li>
                            <li><a href="#"><span class="glyphicon glyphicon-refresh"></span> Update Profile</a></li>
                            <li class="divider"></li>
                            <li><a href="#"><span class="glyphicon glyphicon-off"></span> Sign Out</a></li>
                        </ul><!--end of sub menu-->
                    </li><!--end of dropdown menu-->
                </ul><!end of the user account menu-->
            </div><!--end of collpased nav-->
        </div><!--end of container-->
    </nav><!--end of navbar-->
Update
I have looked into the solution provide by this link, which does not work in the newest version of Bootstrap.
And I have locate the code block which defines the breakpoint of the collapsing effect:
@media (min-width: 768px) {
  .navbar-collapse {
    width: auto;
    border-top: 0;
    -webkit-box-shadow: none;
            box-shadow: none;
  }
  .navbar-collapse.collapse {
    display: block !important;
    height: auto !important;
    padding-bottom: 0;
    overflow: visible !important;
    visibility: visible !important;
  }
  .navbar-collapse.in {
    overflow-y: visible;
  }
  .navbar-fixed-top .navbar-collapse,
  .navbar-static-top .navbar-collapse,
  .navbar-fixed-bottom .navbar-collapse {
    padding-right: 0;
    padding-left: 0;
  }
}
And I tried to modify the defined min-width, however I changed, it just does not work.
 
     
    

 
     
    