Feature new components

[gjssss]

Brief description

• Fix the error and warning in btn-close
• Add a hover dropdown and change the doc

usage is shown in doc

<ul class="inline">
    <li><a href="#">Documentation</a></li>
    <li class="dropdown">
      <div class="dropdown-title">About</div>
      <ul class="dropdown-menu border border-4">
        <li><a href="#">Github</a></li>
        <li><a href="#">Contact</a></li>
      </ul>
    </li>
</ul>

when hover, it will appear. For the issue#249.

Developer Certificate of Origin

• [x] I certify that these changes according to the Developer Certificate of Origin 1.1 as described at https://developercertificate.org/.

Sample pictures

Further details

Add More Components (Maybe from issues).

[gjssss]

Some file was changed, such as package.json and package-lock.json. I don't know how to avoid it and if it may make some problem : ( It is my first PR, if there is any problem, pls ask me! 👍 thx!!

[mef]

A bit of feedback:

• The feature works well in larger screens, and on mobile.
• The drop-down menu's content keeps floating over the rest of navbar links on mobile layout (when the navbar is in collapsed mode), unlike the bootstrap implementation where the dropdown menu pushes the rest of the content down (and can get deactivated on tap).
• An issue is on narrow screens and using a mouse: the drop-down menu is aligned to the left, and cannot be reached as it disappears when the mouse goes towards it and stops hovering on the dropdown title. Situation illustrated in the screenshot below:

[OrangeX4]

Thanks! It is useful for me!