This is an example of an accordion feature on a sidebar menu, designed using HTML, CSS, JavaScript, and Bootstrap framework 4. The font, icons, and Bootstrap styles are imported to the code with their URLs. The concept of Lists has been used with UL and LI components, whereas the UL element has been used with the child elements of LI to display the child elements of the accordion, in an orderly manner. JavaScript methods have been used to implement the collapse feature of the accordion menu. The header of the accordion is given a background color of linear-gradient(#fff, #f1f1f1), which gets changed to linear-gradient(#f1f1f1, #e8e8e8), in a hover event. The cursor style for the accordion items is set as pointer to get the hand cursor effect on hover. The accordion item is given an opacity of 0.7 which gets changed to 1, in a hover event. The child elements of the accordion items are given a background color of #d6dbe0, which gets changed to #007bff, on hover. Source:https://www.tutorialrepublic.com/snippets/preview.php?topic=bootstrap&file=accordion-menu-for-all-purpose