style.css

input:not([type]), input[type=text]:not(.browser-default), input[type=password]:not(.browser-default), input[type=email]:not(.browser-default), input[type=url]:not(.browser-default), input[type=time]:not(.browser-default), input[type=date]:not(.browser-default), input[type=datetime]:not(.browser-default), input[type=datetime-local]:not(.browser-default), input[type=tel]:not(.browser-default), input[type=number]:not(.browser-default), input[type=search]:not(.browser-default), textarea.materialize-textarea{
  color: white;
}


html {
  background: black;
}

select option {
  color:black;
}

body {  
  justify-content: center;
  width: 800px;
  margin-left: auto;
  margin-right: auto;
  padding: 0%;
}

.page-footer .footer-copyright{
  background: white;
}

nav {
  background: white;
}

nav ul a {
  color: black;
}

.btn:hover, .btn-large:hover, .btn-small:hover{
  width: 510px;
  margin-left: 20%;
}
.btn, .btn-large, .btn-small{
  width: 510px;
  margin-left: 20%;
}

header {
  background: white;
  color: black;
  padding: 0 10px 0 10px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 100px;
}

.page-footer {
  background: white;
}

footer {
  background: white;
  margin-top: 100px;
  height: 250px;
}

#login {
  margin: 35%;
}

select{
  background: transparent;
  color:white;
  display: block;
  width: 100%;
}