Cannot set white background to HTML input in Mozilla - html

Question

A strange behavior prevents me from setting white color for an HTML input element's background color (background property) in Mozilla Firefox (it switches to a yellow color). Other colors works fine (black, green). Does anybody know why?
input[type=text] {
width: 100%;
padding: 12px 20px;
margin: 8px 0;
box-sizing: border-box;
border: 1px solid #A6A6A633;
border-radius: 2px;
opacity: 1;
background: white;
color: #9B9B9B;
}
<div class="form-group">
<label for="username">User Name: </label>
<input type="text" id="username" [(ngModel)]="username" placeholder="Enter User Name" name="username">
</div>
EDIT: Since it turned out the problem is caused by Mozilla's autocomplete, it's not a problem anymore since in normal use it changes the background as expected.

Answer 1

In your example the background in perfectly white. I think, there is some other code, that affects your input. Try to make it more specific using the ID #username.
Or, you can use !important rule.
UPDATED
Added the third way. It may be an autocomplete background of browther. Try the code below.
input#username {
width: 100%;
padding: 12px 20px;
margin: 8px 0;
box-sizing: border-box;
border: 1px solid #A6A6A633;
border-radius: 2px;
opacity: 1;
background: #fff !important;
color: #9B9B9B;
}
input#username:-moz-autofill,
input#username:-moz-autofill-preview,
input#username:-webkit-autofill {
filter: none;
background: #fff !important;
}
<div class="form-group">
<label for="username">User Name: </label>
<input type="text" id="username" [(ngModel)]="username" placeholder="Enter User Name" name="username">
</div>

Answer 2

UPDATE
the code listed bellow is not necessary as mentioned in the comments. however refreshing cache helped as the problem came of autocomplete.
OLD
Use background-color: white; and not Background: white;
input[type=text] {
width: 100%;
padding: 12px 20px;
margin: 8px 0;
box-sizing: border-box;
border: 1px solid #A6A6A633;
border-radius: 2px;
opacity: 1;
background-color: white;
color: #9B9B9B;
}