Align a form in navbar-header on small screens with Bootstrap - html

Question

With the following code, on a "middle screen", the result is OK.
But on a small screen (smartphones), it is not.
I wish the input and the submit button (magnifying glass) are aligned on the same line.
How I can do that?
<nav class="navbar navbar-inverse navbar-fixed-top">
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-controls="navbar">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="#">Diko Responsive</a>
</div>
<div id="navbar" class="navbar-collapse collapse">
<form class="navbar-form navbar-right" action="index.php" method="get">
<div class="form-group" >
<input id="terme" name="terme" placeholder="Veuillez saisir un terme" class="form-control input-xs" type="search">
<button type="submit" class="btn btn-info"><span class="glyphicon glyphicon-search"></span></button>
</div>
</form>
</div>
</div>
</nav>
Thanks.
EDIT: I added this CSS file after the advices of #NiklasMH
#media (max-width : 768px){
.form-group input {
width: calc(70% - 32.5px);
}
.form-group button {
width: 40px;
}
}
But as you can see, both are still not aligned.

Answer 1

You almost there. You only forgot to call class=input-group
You no need to add another media queries there.
HTML
<div class="input-group">
<input id="terme" name="terme" placeholder="Veuillez saisir un terme" class="form-control input-xs" type="search">
<span class="input-group-btn">
<button class="btn btn-info" type="button"><span class="glyphicon glyphicon-search"></span></button>
</span>
</div>
Here is the DEMO

Answer 2

I don't know the twitter-bootstrap that good, so this answer is more about what you can do to the CSS.
Bad practice
Some say it's bad practice, but you could eigther use a table to align them on the same row. Then you also can make the left or right column in fixed width like:
td:last-child {
width: 32px;
}
Good practice
Or you can use the calc-value in CSS, which is widly supported now (except in Opera Mini - ref caniuse.com), like:
.form-group input {
width: calc(100% - 44px); /* Minus a little more (4px) than the button-width */
}
.form-group button {
width: 40px;
}
Remember that padding will make the element bigger and force more space, so set box-sizing to border-box (default content-box) to avoid this:
.form-group input, .form-group button {
box-sizing: border-box;
}
JSFIDDLE
.form-group input, .form-group button {
box-sizing: border-box;
}
.form-group input {
width: calc(100% - 44px);
max-width: 160px;
}
.form-group button {
width: 40px;
}
<div class="form-group">
<input placeholder="text"/>
<button>btn</button>
</div>