Address any low-hanging fruit for accessibility

[malini]

Is your feature request related to a problem? Please describe.
In https://github.com/thunderbird/services-ui/ and in Appointment, we should conduct a first pass of known accessibility issues

Describe the solution you'd like
A clear and concise description of what you want to happen.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
We can do a more thorough pass for as part of #299