This is an example of a responsive mailbox layout, designed using CSS, HTML, and Bootstrap framework 4. The images and fonts are imported to the code with their URLs. Media quarries are used to increase the responsiveness of the form. The body of the form is given the styles of font-family as 'Roboto', sans-serif, font-size as .9em, font-weight as 400, and color as #797979. The panelist on the left side is given the styles of line-height as 40px, margin as 5px 0px, padding as 0px 8px, border-radius as 4px, and cursor as pointer to get the hand cursor effect. The panel items take the background color of #fff, in a hover event. The concept of Lists has been used with UL and LI components. UL element has been used with the child elements of LI to display the panel items in an orderly manner. Each mail section is given a different border-left color for identification purposes. Source: