Shrink input field in certain screen sizes with bootstrap - html

Question

I am new to bootstrap.
I try to make a navbar that contains a form and navigation.
I would like to shrink the input field in certain screen sizes.
Right now it looks like this.
This is OK:
In these cases I want to shrink the input field:
Relevant HTML code:
<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-expanded="false" 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="#">Site Name</a>
</div>
<div id="navbar" class="navbar-collapse collapse">
<form class="navbar-form navbar-left">
<div class="form-group">
<input type="text" placeholder="Email" class="form-control">
</div>
<button type="submit" class="btn btn-success">Subscribe</button>
</form>
<ul class="nav navbar-nav navbar-right">
<li class="active">Home</li>
<li>News</li>
<li>Contact</li>
<li class="dropdown">
Dropdown Menu <span class="caret"></span>
<ul class="dropdown-menu">
<li>First Menu Item</li>
</ul>
</li>
</ul>
</div>
</div>
</nav>
How can I achieve this?
Thank you.

Answer 1

You can use this CSS:
.navbar-form .form-control {
width: 100px; // your width
}
#media (min-width: 768px) {
.navbar-form .form-control {
width: 150px; // your width
}
}

Answer 2

Do these changes
In HTML:
<ul id="navbarRight" class="nav navbar-nav navbar-right">
Instead of
<ul class="nav navbar-nav navbar-right">
above is the last.
And add this CSS
#navbar{
width: 100%;
}
form{
max-width: 45%;
}
#navbarRight{
max-width: 55%;
}