HD GUI 2 is a mod for Sonic Adventure DX PC that adds high-resolution textures for almost all menus and GUI items in the game.
To install HD GUI 2 you can use SADX Mod Installer that sets up SADX Mod Loader and downloads the latest versions of mods automatically. The installer can also convert the Steam version of SADX to the 2004 version, which supports the Mod Loader.
SADX Mod Installer: https://sadxmodinstaller.unreliable.network
Alternatively you could install HD GUI 2 manually by downloading the latest build here.
Related mods:
Dreamcast Conversion: https://gitlab.com/PiKeyAr/sadx_dreamcast
Dreamcast DLC: https://gitlab.com/PiKeyAr/sadx-dreamcast-dlc
Sound Overhaul: https://gitlab.com/PiKeyAr/sadx-sound-overhaul
Time of Day: https://gitlab.com/PiKeyAr/sadx-timeofday-mod