This post helps you in building a Input form using bootstrap framework over Visualforce Pages, which is responsive by default

Step 1: Link up Bootstrap Library

You can do this in two ways,

  1. By Adding CDN reference (example explained in this format) &
  2. Uploading Files as Static Resource in Zip Format
<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css" rel="stylesheet" />

Step 2: Add Div Blocks which uses Bootsraps Lib

<apex:form styleClass="form-horizontal" role="form">
    <div class="container">
        <h2>Form Inputs</h2>
        <div class="form-group">
            <label class="control-label col-sm-2" for="email">Email:</label>
            <div class="col-sm-10">
               <apex:inputField value="{!email}" styleClass="form-control" id="email" html-placeholder="Email Address">
            </div>
        </div>
        <div class="form-group">
            <label class="control-label col-sm-2" for="pwd">Password:</label>
            <div class="col-sm-10">
                <apex:inputField value="{!pass}" styleClass="form-control" id="pwd" html-placeholder="Enter password">
            </div>
        </div>
        <div class="form-group">
            <div class="col-sm-offset-2 col-sm-10">
                <button type="submit" class="btn btn-default">Submit</button>
            </div>
        </div>
    </div>
</apex:form>

That'a it you're good to go now, you know What this page works for
Web, Desktop, Table & Mobile YaY!!!

Sample Output (Desktop & Mobile)

Comment me, for suggestions or any help needed