CSS Input type=text

I need some help with css on my login. I want the yellow background color to be transparent when a username is selected, or the two .svg pictures to come over the yellow background.

Two Links of what I mean:

http://zanterite.club/before.png

http://zanterite.club/after.png

I want the svgs of the username and password in the before picture to show in the after picture.

My code

css:

.user{
background-image: url("css/user.svg");
background-size: 18px 18px;
background-position: 11px 8px;
background-repeat: no-repeat;
}
.pass{
background-image: url("css/pass.svg");
background-size: 18px 18px;
background-position: 11px 8px;
background-repeat: no-repeat;
}

html:

<form>
<input type="text" placeholder="username" class="user" name="username" />
<input type="password" placeholder="password" class="pass" name="password" />
<input type="submit" value="LOGIN" />
</form>