W3.CSS Panels:

In W3.CSS, a panel is very similar to a container but with a great difference: Panels do have a margin of 16px in the top and bottom. Note that containers didn’t had margins. They only had padding of 16px in the left and right. We simply add a class w3-panel along with a colour to the <div> tag.

Using class w3-panel and w3-color:

<div class="w3-panel w3-indigo">
   <h2>India</h2>
   <p>India is a great country. Geographically it is located in South Asia.</p>
</div>

Here, the class w3-panel makes a panel and, the class w3-indigo puts an indigo background to the div.
Output:

Using classes w3-leftbar, w3-xlarge and w3-serif to make it look like a quote:

<div class="w3-panel w3-pale-pink w3-leftbar w3-xlarge w3-serif">
   <p><i>Love for all, hatred for none.</i></p>
</div>

Here, serif means to the font with fine edges like ‘ T ’. w3-leftbar creates a gray left-bar and w3-xlarge makes it thick.
Output:

Using the class w3-card-4 to make it look like a card:

<div class="w3-panel w3-orange w3-card-4">
  <h2>India</h2>
  <p>India is a great country. Geographically it is located in South Asia.</p>
</div>

Cards appear with a general shadow. Here 4 is a shadow parameter. 2 will make a little smaller shadow.
Output:

Using the class w3-round-size to make a rounded corner panel:

<div class="w3-panel w3-pink w3-round-xlarge">
  <h2>India</h2>
  <p>India is a great country. Geographically it is located in South Asia.</p>
</div>

The size parameters in w3-round-size are-

small
large
xlarge
xxlarge

Output: