Collapsing panels up and down with icons (yet the official Bootstrap example has no icons).

∖2212 - minus
∖002b - plus

∖e160 - collapse-up
∖e159 - collapse-down

∖e080 - shevron-right
∖e114 - shevron-down

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The code:
--
.panel-heading .accordion-toggle:after {
/* symbol for "opening" panels */
font-family: 'Glyphicons Halflings'; /* essential for enabling glyphicon */
content: "∖e114"; /* from bootstrap.css */
float: right;
color: grey;
}
.panel-heading .accordion-toggle.collapsed:after {
/* symbol for "collapsed" panels */
content: "∖e080"; /* from bootstrap.css */
}