CSS issue, when filling in a form the header goes up - css

Question

I have a strange CSS issue, I'm not quite sure how to fix this.
When I press the "Sign In" button on my website and I start to type in the Username, the header goes up. I really don't know what is causing this.
Any ideas?
Thanks!
Here is some code:
The form:
.tooltip-wrap {
position: fixed;
display:none;
}
.tooltip-wrap .corner {
position:relative;
z-index:100;
margin-left:-5px;
width:0;
height:0;
border:5px solid transparent;
border-bottom-color:#fff;
}
.tooltip-text {
float:left;
margin-left:-50%;
padding:1em 15px;
background:#fff;
color:#333;
}
This is the part that goes up:
.header-navigation.back {
z-index:-1;
position:absolute;
margin-left:0;
margin-top:-6px;
border:none;
display:block; height:137px; width:1171px; padding:0px; outline:none; text-indent:-9999px;
background-image:url('xhttp://frenchegg.com/images/backmenu.png');
}
You need to click on Username and start typing something.

Answer 1

Very strange bug, and I can't explain what's going on. But it is related to your div.header-navigation.back. If you remove that, the behaviour disappears.
As far as I can tell, you are only using that element for your background image, so it's not a good idea to include it in the markup anyway. If you amend your .site-header you can achieve the same effect without the extra div:
.site-header {
background: #0894ff url('http://frenchegg.com/images/backmenu.png') 50% 20px no-repeat;
background: url('http://frenchegg.com/images/backmenu.png') 50% 20px no-repeat,
linear-gradient(to bottom, rgba(255,255,255,0.1) 0%,rgba(255,255,255,0) 100%);
}
I couldn't quite work out what you're trying to achieve with your gradient, but the idea would be to provide multiple backgrounds for those browsers that support them, with a fallback to a solid colour.

Answer 2

Change the line-height of the input box - fixes the issue.
HTML to change:
<input type="text" id="text-user" name="user_login" value="Username" style="
line-height: 15px;
">
CSS:
#text-user{
line-height: 15px;
}
The reason is because the line-height of the input was much smaller without text, than it was with text. So when you typed something into the box, the line-height expanded which is what caused the header to be pushed up.
Edit
I see you're having no luck with the code, so do these two more things and you're sure to be up and running - it's working here for me.
Remove the following from .site-header:
padding: 2em 0;
Next, change the row style to look like this:
.row{
margin: 0 auto;
padding: 0 30px;
width: 1171px;
height: 137px;
}

Answer 3

I think the solution is along these lines:
Set .header-wrap to have overflow:visible (well, remove overflow hidden!) - this will mean you have to slice those character graphics to have flat bottoms.
Then, change .tooltip-wrap to be position:absolute;z-index:2; (not fixed).
I also noticed that you have the placeholder polyfill in your head. This means you could use that attribute on the input rather than value; like so:
<input type="text" name="user_login" placeholder="Username">
Very cute site!

Answer 4

You could give it a z-index instead of a fixed position, and give it an absolute position.