This is an example of a product filter with an accordion feature and checkboxes, designed using HTML, CSS, and Bootstrap framework 4. Media quarries have been used to increase the responsiveness of the form. The body of the form is given a background color of #f5f6f7. The panel heading is given the styles of font-family as 'Glyphicons Halflings, display as block, padding as 10px, color as #555, font-size as 11px, text-transform as uppercase to automatically convert the text to uppercase, letter-spacing as 1px, and word-spacing as 3px. The panel heading is given a transform style of rotate(180deg) to implement the collapsible effect. The checkboxes are given a height and a width of 24px, font color #fff, cursor style as pointer to get the hand cursor effect in a hover event. The checkboxes take the color of #9faab7 in a hover event, and #2874ef in a checked event. The checkbox text is given a font-family of "Font Awesome 5 Free, and a font-size of 14.66667px. The Refine search button is given a background color of #2874ef, and a font-size as 12px. Source:https://bbbootstrap.com/snippets/refine-product-filter-sidebar-collapse-accordion-custom-checkbox-98247635