index.css

.logo{
  width: 100%;
  background-color: #fff;
}

#logo_image {
	display: block;	
	margin-left: auto;
	margin-right: auto;
}

.login_form{
  display: table;
  margin: 0 auto;
  padding-top: 10%;
  padding-left: 10%;
  zoom: 0.90;
  -moz-transform: scale(0.90);
}


@media (min-width: 768px){
    .navbar-nav{
        float:none;
        margin: 0 auto;
        display: table;
        table-layout: fixed;
        z-index: 100;
    }
}

video#bgvid { 
    position: fixed;
    top: 50%;
    left: 50%;
    min-width: 100%;
    min-height: 100%;
    width: auto;
    height: auto;
    z-index: -100;
    -ms-transform: translateX(-50%) translateY(-50%);
    -moz-transform: translateX(-50%) translateY(-50%);
    -webkit-transform: translateX(-50%) translateY(-50%);
    transform: translateX(-50%) translateY(-50%);
    background: url(poster.png) no-repeat;
    background-size: cover;
  }

.p_inicial {
  color: #fff;
  font-size: 5em;
  text-align: center;
  font-family: sans-serif;
}

.initial_container{
  margin-top: 5%;
}

@media screen and (max-device-width: 800px) {
    html {
         background: url(polina.jpg) #000 no-repeat center center fixed;
    }
    #bgvid {
        display: none;
    }
}