fix: reformat navigation bar and background

[Revathyvenugopal162]

partially fixes the navigation bar design updates #403

• updated the navigation background

• updated the font color, font size and hovering color of navigation

• updated the font size , font color and overall body background

• updated transparent logos

[Revathyvenugopal162]

@ansys/pyansys-core I have added the logo naming suggested by @klmcadams and will proceed with merging this PR.

[RobPasMue]

Oh well - you already merged it @Revathyvenugopal162...

[Revathyvenugopal162]

Oh well - you already merged it @Revathyvenugopal162...

yeah, i will open an overall PR to add docs and warnings with logos and all upcoming changes.