An SVG image would be the best
In my opinion the new log does not fit, because the yellowish color clashes with the back ground. Of course this can be adjusted, and also making a shadow would be possible.
Regarding the website design: I my opinion it has some weaknesses, especially for people with impairments / disabilities, but in general i like it. If some one provides a new theme, i think no one would be against this. Making it switchable would be an option too then
WorldSavior: Every browser has an option like 'inspect Element' if you make a right click on the page. There you can change the css temporarily, e.g. the background-color (and background-image) of the page is defined for the <body> tag. I think some browsers do also allow custom css settings for a specific website.