How to change (-,+) symbol with a button Bootstrap Accordion?
In your example you are using the div.card-header as the collapse toggle; Do you intend on limiting the toggle trigger to the button only? If so, consider changing your a.card-title to div.card-title and add your button within. Then adjust your css to .card-header button:after. Please note you should only use the href attribute on an anchor tag (you have it on your div.card-header) and for the button element you would use data-target. You can review the documentation here.
If your intent is to have more complex markup (not just plain text label) then you will need a js solution. (I can assist with that as well)
HTH
.accordion .card-header button:after {
font-family: 'FontAwesome';
content: "\f068";
}
.accordion .card-header button.collapsed:after {
content: "\f067";
}<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
<div class="container">
<div id="accordion" class="accordion">
<div class="card mb-0">
<div class="card-header">
<div class="card-title">
Item 1
<button type="button" class="btn btn-primary float-right collapsed" data-toggle="collapse" data-target="#collapseOne"></button>
</div>
</div>
<div id="collapseOne" class="card-body collapse" data-parent="#accordion" >
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</p>
</div>
<div class="card-header">
<div class="card-title">
Item 2
<button type="button" class="btn btn-primary float-right collapsed" data-toggle="collapse" data-target="#collapseTwo"></button>
</div>
</div>
<div id="collapseTwo" class="card-body collapse" data-parent="#accordion" >
<p>Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt
aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat
craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
</p>
</div>
</div>
</div>
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