The type of operating system and hosting doesn’t matter much for design, but the platform is a factor. For instance, if you need a WordPress theme, the designer must work with WordPress themes and customize them in a way that a developer can feasibly code in CSS or JavaScript on the front end. If you use another CMS, the developer must work with those elements. Most designers specialize in specific platforms, so review their portfolios and experience for specific platforms before you invite them to bid on your project.
The 2014 case involving Peapod, an online grocery retailer emphasizes that being ADA compliant goes beyond your website. The settlement required Peapod to make its mobile applications accessible by March 2015 and its website accessible by September 2015. Since mobile apps are fast becoming the preferred method of online shopping, e-commerce sites must focus on app accessibility too. 
Hey OB – Disclaimer – none of this is legal advice and you’d want to check with a lawyer to know if you’re at risk for any action if you’re not ADA compliant. Based on what we’ve seen if you don’t have a physical retail or service location, and you don’t receive any funding from the government you likely aren’t required to have a website that would be considered compliant. Some people expect that to change in the next few years, but that’s what we know for now. Let us know if you have more questions or would like to test your site.
ADA website compliance is about making sure that everyone has equal access to all the elements on your website and apps. That may mean you need to provide alternatives for some of the functions and content on your site in order to meet ADA website compliance standards. Here’s a quick rundown of some of the accommodations that need to be incorporated into your website to meet the ADA guidelines:

Toyota Motor Manufacturing, Kentucky, Inc. v. Williams,[72] was a case in which the Supreme Court interpreted the meaning of the phrase "substantially impairs" as used in the Americans with Disabilities Act. It reversed a Sixth Court of Appeals decision to grant a partial summary judgment in favor of the respondent, Ella Williams, that qualified her inability to perform manual job-related tasks as a disability. The Court held that the "major life activity" definition in evaluating the performance of manual tasks focuses the inquiry on whether Williams was unable to perform a range of tasks central to most people in carrying out the activities of daily living. The issue is not whether Williams was unable to perform her specific job tasks. Therefore, the determination of whether an impairment rises to the level of a disability is not limited to activities in the workplace solely, but rather to manual tasks in life in general. When the Supreme Court applied this standard, it found that the Court of Appeals had incorrectly determined the presence of a disability because it relied solely on her inability to perform specific manual work tasks, which was insufficient in proving the presence of a disability. The Court of Appeals should have taken into account the evidence presented that Williams retained the ability to do personal tasks and household chores, such activities being the nature of tasks most people do in their daily lives, and placed too much emphasis on her job disability. Since the evidence showed that Williams was performing normal daily tasks, it ruled that the Court of Appeals erred when it found that Williams was disabled.[72][73] This ruling is now, however, no longer good law—it was invalidated by the ADAAA. In fact, Congress explicitly cited Toyota v. Williams in the text of the ADAAA itself as one of its driving influences for passing the ADAAA.
ADA disabilities include both mental and physical medical conditions. A condition does not need to be severe or permanent to be a disability.[6] Equal Employment Opportunity Commission regulations provide a list of conditions that should easily be concluded to be disabilities: deafness, blindness, an intellectual disability (formerly termed mental retardation), partially or completely missing limbs or mobility impairments requiring the use of a wheelchair, autism, cancer, cerebral palsy, diabetes, epilepsy, Human Immunodeficiency Virus (HIV) infection, multiple sclerosis, muscular dystrophy, major depressive disorder, bipolar disorder, post-traumatic stress disorder, obsessive compulsive disorder, and schizophrenia.[7] Other mental or physical health conditions also may be disabilities, depending on what the individual's symptoms would be in the absence of "mitigating measures" (medication, therapy, assistive devices, or other means of restoring function), during an "active episode" of the condition (if the condition is episodic).[7]

The ADA statute identifies who is a person with a disability, who has obligations under the ADA, general non-discrimination requirements and other basic obligations. It delegates fleshing out those obligations to federal agencies. The agencies issue regulations and design standards. The regulations have the details on the rights of people with disabilities and responsibilities of employers, state and local governments, transportation providers, businesses and non-profit organizations. The design standards specify how many entrances need to be accessible, how many toilet rooms and the design for those elements.  To know what the ADA requires, you need to read the law, regulations and design standards.  
This is particularly important when working for a government agency or government contractor, as these organizations must follow web accessibility guidelines under Section 508 of the Workforce Rehabilitation Act of 1973. Although ADA and Section 508 compliance are different, the published checklist for Section 508 compliance offers insight into ways to make websites accessible for people with disabilities, and thereby work toward ADA compliance.
For most businesses, the need for ADA web compliance means they will need to make at least some adjustments to all of their online marketing strategies. For instance, if your company provides tax preparation services, all of the tax forms you provide for customers to download would need to meet accessibility standards. Any online tax preparation services that you offer would also need to be configured so they meet ADA standards, as would your mobile app.
Because the ADA establishes overlapping responsibilities in both EEOC and DOJ for employment by State and local governments, the Federal enforcement effort is coordinated by EEOC and DOJ to avoid duplication in investigative and enforcement activities. In addition, since some private and governmental employers are already covered by nondiscrimination and affirmative action requirements under the Rehabilitation Act of 1973, EEOC, DOJ, and the Department of Labor similarly coordinate the enforcement effort under the ADA and the Rehabilitation Act.
Blind people, those with low vision, and people with other disabilities that affect their ability to read a computer display often use different technologies so they can access the information displayed on a webpage. Two commonly used technologies are screen readers and refreshable Braille displays. As discussed above, a screen reader is a computer program that speaks the text that appears on the computer display, beginning in the top-left corner. A refreshable Braille display is an electronic device that translates text into Braille characters that can be read by touch. These assistive technologies read text. They cannot translate images into speech or Braille, even if words appear in the images. For example, these technologies cannot interpret a photograph of a stop sign, even if the word “stop” appears in the image.
The Department has assembled an official online version of the 2010 Standards to bring together the information in one easy-to-access location.  It provides the scoping and technical requirements for new construction and alterations resulting from the adoption of revised 2010 Standards in the final rules for Title II (28 CFR part 35) and Title III (28 CFR part 36).
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