To view the history of cases that a specific customer has submitted, the representative should go through the following hierarchy of information: All Accounts > Account Detail > Contact Detail > Case Related List. This is because cases are related to contacts, and contacts are related to accounts. By navigating from the account level to the contact level, the representative can see all the contacts associated with a specific account. Then, by selecting a contact, the representative can see the case related list, which shows all the cases that the contact has submitted or been involved in. This way, the representative can view the history of cases for a specific customer in a logical and efficient manner.Reference: : UX Designer Certification Prep: Designing with Service Cloud | Trailhead : Service Cloud Basics | Salesforce Help

The Lightning component that should be used to organize content into collapsible sections is theAccordioncomponent. The Accordion component displays vertically stacked sections of content that can be expanded and collapsed by clicking on the section headers. Users can control how much content is visible at once, and don't need to scroll as much to see the content of a page. The Accordion component can also be configured to allow multiple sections to be open at the same time. The Accordion component implements the accordion blueprint in the Salesforce Lightning Design System (SLDS).Reference:

:lightning-accordion - documentation - Salesforce Lightning Component Library

:Collapsible Related List in Lightning Experience

:How To Create Expand/Collapse Sections In SFDC Lightning Component

The Lightning Accordion component isdesigned to help create an organized, collapsible display of content. It is composed of a header and a body, which can be used to display different sections of content in an organized way. The body of the Accordion is hidden until the header is clicked, allowing the user to quickly and easily access the content they need. Salesforce provides a detailed guide to using the Accordion component, including examples and code snippets, which can be found here:https://developer.salesforce.com/docs/component-library/documentation/lwc/lwc.use_accordion.

The two UX design principles that are key to creating excellent mobile user experiences are:

Consistency across device experiences. This means that the design of a mobile app or website should match the design of the desktop version, as well as other platforms and devices. Consistency helps users to recognize and trust the brand, as well as to navigate and use the product more easily.Consistency also reduces the cognitive load and confusion for users who switch between different devices12

Prioritization of content and UI elements on the screen. This means that the design of a mobile app or website should focus on the most important and relevant information and actions for the user, and eliminate or minimize the unnecessary or secondary ones. Prioritization helps users to achieve their goals faster and more efficiently, as well as to avoid distractions and clutter.Prioritization also improves the readability and usability of the product on smaller screens34

https://uxcam.com/blog/mobile-ux/ https://uxplanet.org/mobile-ux-design-key-principles-dee1a632f9e6

Designing perceivable content means that the content should be presented in a way that can be convertible between different formats, so that users with different sensory abilities can access it. For example, providing text alternatives for images and videos, captions and transcripts for audio, and audio descriptions for visual content. This way, users who are blind, deaf, or have low vision or hearing can perceive the content using assistive technologies, such as screen readers, braille keyboards, or captions. The content should not only be presented in a visual format (A) or an audio format (B), as that would exclude users who cannot see or hear the content.The content should be adaptable to different formats and devices, and follow the Web Content Accessibility Guidelines (WCAG) principle of perceivability12.Reference:

Perceivable - Accessibility | MDN

What Is Perceivability in Web Accessibility? WCAG Principles Explained

To create visual consistency with regard to alignments, grids, spacing, and typography, the part of the Salesforce Lightning Design System (SLDS) that should be used is utility classes. Utility classes are CSS classes that provide common styling properties, such as margins, paddings, borders, colors, fonts, and text alignments. Utility classes can be applied to any HTML element to quickly and easily adjust its appearance and layout. Utility classes follow the BEM (Block Element Modifier) naming convention, which makes them easy to read and understand. Utility classes can help the designer to create visual consistency across the Lightning components and pages, without writing custom CSS or overriding the component blueprints.Reference: : Utility Classes | Lightning Design System : UX Designer Certification Prep: Designing with Lightning Design System | Trailhead