Using Chrome on such an old OS today is largely a "legacy" experience:
(Recommended): If your Mac hardware supports it, upgrade to a newer macOS version (e.g., macOS Catalina 10.15 or later) to run the latest secure version of Chrome. google chrome free download for mac os x 10.9.5
No. Dark mode in Chrome requires macOS 10.14 Mojave or later. Using Chrome on such an old OS today