Base rules are the defaults. They are almost exclusively single element selectors but it could include attribute selectors, pseudo-class selectors, child selectors or sibling selectors.
<h1>Heading 1</h1>
<h2>Heading 1</h2>
<h3>Heading 1</h3>
<a href="http://example.com">Example</a>
Button styles can be applied to any element. Typically you'll want to
use either a <button> or an <a> element:
<button class="btn btn-default">Click</button>
<a class="btn btn-default" href="#">Me!</a>
Use any of the available button classes:
<!-- Standard button -->
<button type="button" class="btn btn-default">Default</button>
<!-- Provides extra visual weight and identifies the primary action in a set of buttons -->
<button type="button" class="btn btn-primary">Primary</button>
Add .btn-lg or .btn-sm for different button sizes:
<p>
<button type="button" class="btn btn-primary btn-lg">Large button</button>
</p>
<p>
<button type="button" class="btn btn-primary">Default button</button>
</p>
<p>
<button type="button" class="btn btn-primary btn-sm">Small button</button>
</p>
Put labels before form element, with a for="" property or around it:
<p>
<label for="input_id">Label</label> <input type="text" id="input_id">
</p>
<p>
<label>Wrapping Label <input type="text"></label>
</p>