From the author's README on Thunderstore

A custom UI theme featuring atmospheric backgrounds, dark visuals, and a crimson color scheme.

Features

Custom menu and character customization backgrounds
Updated UI colors
Darker visual styling

Work in Progress

Infernal UI is still in development. This initial release establishes the foundation for the theme, with additional visual changes and refinements planned for future updates.

Compatibility

Other UI mods that modify the same assets may conflict with Infernal UI. Load order determines which replacements take priority.

Install Infernal UI

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Infernal UI and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.