https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_accordion
button.accordion:after {
content: '\002B';
color: #777;
font-weight: bold;
float: right;
margin-left: 5px;
}
.arrow-down {
width: 0;
height: 0;
border-left: 20px solid transparent;
border-right: 20px solid transparent;
border-top: 20px solid #f00;
}
https://www.w3schools.com/howto/howto_js_accordion.asp
https://www.w3schools.com/howto/howto_css_arrows.asp
https://freefrontend.com/css-arrows/
accordion show css js arrow