Wrap text into a shade box in blogger

blockquote {
color: #888;
border: 2px solid #333;
padding: 10px;
background-color: #ccc;
}

put above codes into the style.css.

Or  write below codes in the the html post.

<blockquote style="border: 2px solid #666; padding: 10px; background-color: #ccc;"> This is some quoted text.</blockquote>

Reference:
https://www.bloggingbasics101.com/how-do-i-make-s/
https://www.rapidtables.com/web/color/html-color-codes.html