diff --git a/src/ui/ColorManager.ts b/src/ui/ColorManager.ts
index 6d68c58d..923b2823 100644
--- a/src/ui/ColorManager.ts
+++ b/src/ui/ColorManager.ts
@@ -3,8 +3,7 @@
  * @license MIT
  */
 
-import { IColorManager, IColor, IColorSet } from './Types';
-import { ITheme } from 'xterm';
+import { IColorManager, IColor, IColorSet, ITheme } from './Types';
 
 const DEFAULT_FOREGROUND = fromHex('#ffffff');
 const DEFAULT_BACKGROUND = fromHex('#000000');
@@ -90,7 +89,11 @@ export class ColorManager implements IColorManager {
     const canvas = document.createElement('canvas');
     canvas.width = 1;
     canvas.height = 1;
-    this._ctx = canvas.getContext('2d');
+    const ctx = canvas.getContext('2d');
+    if (!ctx) {
+      throw new Error('Could not get rendering context');
+    }
+    this._ctx = ctx;
     this._ctx.globalCompositeOperation = 'copy';
     this._litmusColor = this._ctx.createLinearGradient(0, 0, 1, 1);
     this.colors = {
@@ -133,11 +136,11 @@ export class ColorManager implements IColorManager {
   }
 
   private _parseColor(
-    css: string,
+    css: string | undefined,
     fallback: IColor,
     allowTransparency: boolean = this.allowTransparency
   ): IColor {
-    if (!css) {
+    if (css === undefined) {
       return fallback;
     }
 
diff --git a/src/ui/Types.ts b/src/ui/Types.ts
index ef725ba6..b7b0ac21 100644
--- a/src/ui/Types.ts
+++ b/src/ui/Types.ts
@@ -20,3 +20,27 @@ export interface IColorSet {
   selection: IColor;
   ansi: IColor[];
 }
+
+export interface ITheme {
+  foreground?: string;
+  background?: string;
+  cursor?: string;
+  cursorAccent?: string;
+  selection?: string;
+  black?: string;
+  red?: string;
+  green?: string;
+  yellow?: string;
+  blue?: string;
+  magenta?: string;
+  cyan?: string;
+  white?: string;
+  brightBlack?: string;
+  brightRed?: string;
+  brightGreen?: string;
+  brightYellow?: string;
+  brightBlue?: string;
+  brightMagenta?: string;
+  brightCyan?: string;
+  brightWhite?: string;
+}
diff --git a/src/ui/tsconfig.json b/src/ui/tsconfig.json
index b3613eef..e07bd9c3 100644
--- a/src/ui/tsconfig.json
+++ b/src/ui/tsconfig.json
@@ -10,12 +10,8 @@
       "../../node_modules/@types/mocha"
     ]
   },
-  "include": [
-    "./Lifecycle.ts",
-    "./RenderDebouncer.ts",
-    "./ScreenDprMonitor.ts"
-  ],
+  "include": [ "./**/*" ],
   "references": [
     { "path": "../common" }
   ]
-}  
\ No newline at end of file
+}