CSS takes to load in window resize

It's a beginner question yet, I'm using the materialize framework and I'm having a problem that when I slow down or increase the window some elements take a long time for the css to load, or sometimes I need to refresh the page to load the css of an element specific. In this case it is an icon that leaves its position when the window resizes. I wanted to know if anyone can help me avoid this. This is the code for the login button, where it stays

<a class="dropdown-button right" href="#!" data-activates="dropdown-login" 
   data-beloworigin="true" id="btn-header">          
        <span id="text-drop">
             Login
        </span>
        <i class="mdi mdi-account right"></i>
        <i class="mdi mdi-menu-down right" id="down-arrow"></i>        
</a>

CSS CODE

#btn-header .mdi-account{
    margin-left: 5px !important;
    display: inline-block !important;
    float: none !important;
    width: 20px !important;
}
#btn-header .mdi-menu-down{
    margin-left: -5px !important;
    display: inline-block !important;
    float: none !important;
}