Add horizontal scrollbar to html table

First, make a display: block of your table

then, set overflow-x: to auto.

table {
    display: block;
    overflow-x: auto;
    white-space: nowrap;
}

Nice and clean. No superfluous formatting.

Here are more involved examples with scrolling table captions from a page on my website.

If an issue is taken about cells not filling the entire table, append the following additional CSS code:

table tbody {
    display: table;
    width: 100%;
}

Did you try CSS overflow property?

overflow: scroll; /* Scrollbar are always visible */
overflow: auto;   /* Scrollbar is displayed as it's needed */

UPDATE
As other users are pointing out, this is not enough to add the scrollbars.
So please, see and upvote comments and answers below.

Wrap the table in a DIV, set with the following style:

div.wrapper {
  width: 500px;
  height: 500px;
  overflow: auto;
}