Fix website accessibility

[cheng-tan]

Why are these changes needed?

Fix accessibility issue for the website

TODO:

• fix light theme accessibility issue
• fix dark them accessibility issue

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (260e0cf) 31.98% compared to head (ac058be) 31.98%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1153   +/-   ##
=======================================
  Coverage   31.98%   31.98%           
=======================================
  Files          33       33           
  Lines        4415     4415           
  Branches     1030     1030           
=======================================
  Hits         1412     1412           
  Misses       2887     2887           
  Partials      116      116           

Flag	Coverage Δ
unittests	31.93% <ø> (ø)

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[skzhang1]

The default appearance should not be dark. Can you change it to light? Thanks! @cheng-tan

[cheng-tan]

The default appearance should not be dark. Can you change it to light? Thanks! @cheng-tan

Hi @skzhang1, is your system set to dark theme? I didn't change the default color mode, so it should still be light

[victordibia]

Thanks for the color contrast fixes @cheng-tan!
I was able to run without any errors.
Looking good!

[skzhang1]

The default appearance should not be dark. Can you change it to light? Thanks! @cheng-tan

Hi @skzhang1, is your system set to dark theme? I didn't change the default color mode, so it should still be light

Today I learned. My system is dark theme.