Space Donkey

Here is an example of how to pimp the collapse-o-matic expand to use a grey bar style using CSS.
Be sure you are using the div ad your default tag in the plugin settings.

The CSS:

.greybar {
   border: 1px dotted #aaaaaa;
   padding: 7px;
   background-position: 98% center;
   background-color: #cccccc;
}

The Code:

[expand trigclass="arrowright greybar" title="Monkeys Are Fast"]...[/expand]

To give the target content a border, use the targclass attribute:

The CSS:

.blueborder {
   border: 1px dotted blue;
   border-top: none;
   margin-left: 0;
  padding: 5px;
}

The Code:

[expand trigclass="arrowright greybar" targclass="blueborder" title="Monkeys Are Fast"]...[/expand]

.de_flag {
    background-image: url(https://lipis.github.io/flag-icon-css/flags/4x3/de.svg);
    background-size: 64px 16px;
    background-repeat: no-repeat;
    background-position: -10px center;
    padding: 7px 7px 7px 42px;
}

then add the new class to the trigclass attribute:

[expand trigclass="arrowright greybar de_flag" title="Deutschland"]...[/expand]

Shortcode

This is an example of some text that has a trigger placed inline, meaning that the trigger does not break the flow of the text. However, when this triggerhidden content is clicked and the target is expanded, the target would break the paragraph as a display: block element. Naturally, when the element is collapsed, the inline flow returns.

...However, when [expand tag="span" title="this trigger" targtag="span"]hidden content[/expand] is clicked...

The Roll-Your-Own Method

This is an example of some text that has a trigger placed inline, using the roll-your-own method. However, when this trigger

is clicked and the target is expanded, the target would break the paragraph as a display: block element. Naturally, when the element is collapsed, the inline flow returns.

...However, when <span title="this trigger" class="collapseomatic" id="testme2">this trigger</span><div class="collapseomatic_content" id="target-testme2">hidden content</div>
is clicked...