Marker info window styles seem to be currently broken. This issue is related to #435, because changing the version property offers a temporary fix. Below are some version-specific screenshots:

version="3.34", info window and icons still styled correctly:

version="3.35", icon styles broken:

version="3.36", both info window and icon styles broken:

Currently working version 3.34 seems to go offline after mid-May, so switching the version as a workaround is only temporary. Here is a link to JSFiddle for reproducing the issue:

https://jsfiddle.net/jlaamanen/1djn28zu/3/