Made requested accessibility changes. (#20318)
### Description
Made requested changes from Accessibility audit. Live at:
[maanavd.github.io/onnxruntime/](https://maanavd.github.io/onnxruntime/)
### Motivation and Context
Related issues addressed:
#20259, #20261, #20263, #20264, #20096, #20100, #20101, #20102, #20103,
#20119, #20120, #20123
Co-authored-by: MaanavD <maanavdalal@microsoft.com>
