diff --git a/types/jss/css.d.ts b/types/jss/css.d.ts
index 3f01be6a62..3e5f81c582 100644
--- a/types/jss/css.d.ts
+++ b/types/jss/css.d.ts
@@ -1,130 +1,134 @@
 // These CSS typings adapted from TypeStyle: https://github.com/typestyle/typestyle
 
-import { Observable } from './observable'
-import * as csstype from 'csstype'
+import { Observable } from './observable';
+import * as csstype from 'csstype';
+
+type Length = string | number;
 
 export type ObservableProperties<P> = {
-  [K in keyof P]: P[K] | Observable<P[K]>
-}
+    [K in keyof P]: P[K] | Observable<P[K]>
+};
 
 export type CSSProperties =
-	& ObservableProperties<csstype.Properties<string | number>>
-	& ObservableProperties<csstype.PropertiesHyphen<string | number>>;
+	& ObservableProperties<csstype.Properties<Length>>
+	& ObservableProperties<csstype.PropertiesHyphen<Length>>;
 
 export interface JssProps {
-	'@global'?: CSSProperties;
-	extend?: string;
-	composes?: string | string[];
+    '@global'?: CSSProperties;
+    extend?: string;
+    composes?: string | string[];
 }
 
 export interface JssExpand {
-	animation:
-		| {
-				delay: CSSProperties['animationDelay'];
-				direction: CSSProperties['animationDirection'];
-				duration: CSSProperties['animationDuration'];
-				iterationCount: CSSProperties['animationIterationCount'];
-				name: CSSProperties['animationName'];
-				playState: CSSProperties['animationPlayState'];
-				timingFunction: any;
-			}
-		| CSSProperties['animation'];
-	background:
-		| {
-				attachment: CSSProperties['backgroundAttachment'];
-				color: CSSProperties['backgroundColor'];
-				image: CSSProperties['backgroundImage'];
-				position: CSSProperties['backgroundPosition'] | number[]; // Can be written using array e.g. `[0 0]`
-				repeat: CSSProperties['backgroundRepeat'];
-				size: Array<CSSProperties['backgroundSize'] | CSSProperties['backgroundSize']>; // Can be written using array e.g. `['center' 'center']`
-			}
-		| CSSProperties['background'];
-	border:
-		| {
-				color: CSSProperties['borderColor'];
-				style: CSSProperties['borderStyle'];
-				width: CSSProperties['borderWidth'];
-			}
-		| CSSProperties['border'];
-	boxShadow:
-		| {
-				x: any;
-				y: any;
-				blur: any;
-				spread: any;
-				color: CSSProperties['color'];
-				inset?: 'inset'; // If you want to add inset you need to write "inset: 'inset'"
-			}
-		| CSSProperties['boxShadow'];
-	flex:
-		| {
-				basis: CSSProperties['flexBasis'];
-				direction: CSSProperties['flexDirection'];
-				flow: CSSProperties['flexFlow'];
-				grow: CSSProperties['flexGrow'];
-				shrink: CSSProperties['flexShrink'];
-				wrap: CSSProperties['flexWrap'];
-			}
-		| CSSProperties['flex'];
-	font:
-		| {
-				family: CSSProperties['fontFamily'];
-				size: CSSProperties['fontSize'];
-				stretch: CSSProperties['fontStretch'];
-				style: CSSProperties['fontStyle'];
-				variant: CSSProperties['fontVariant'];
-				weight: CSSProperties['fontWeight'];
-			}
-		| CSSProperties['font'];
-	listStyle:
-		| {
-				image: CSSProperties['listStyleImage'];
-				position: CSSProperties['listStylePosition'];
-				type: CSSProperties['listStyleType'];
-			}
-		| CSSProperties['listStyle'];
-	margin:
-		| {
-				bottom: CSSProperties['marginBottom'];
-				left: CSSProperties['marginLeft'];
-				right: CSSProperties['marginRight'];
-				top: CSSProperties['marginTop'];
-			}
-		| CSSProperties['margin'];
-	padding:
-		| {
-				bottom: CSSProperties['paddingBottom'];
-				left: CSSProperties['paddingLeft'];
-				right: CSSProperties['paddingRight'];
-				top: CSSProperties['paddingTop'];
-			}
-		| CSSProperties['padding'];
-	outline:
-		| {
-				color: CSSProperties['outlineColor'];
-				style: 'none' | 'hidden' | 'dotted' | 'dashed' | 'solid' | 'double' | 'groove' | 'ridge' | 'inset' | 'outset';
-				width: any;
-			}
-		| CSSProperties['outline'];
-	textShadow:
-		| {
-				x: any;
-				y: any;
-				blur: any;
-				color: CSSProperties['color'];
-			}
-		| CSSProperties['textShadow'];
-	transition:
-		| {
-				delay: CSSProperties['transitionDelay'];
-				duration: CSSProperties['transitionDuration'];
-				property: CSSProperties['transitionProperty'];
-				timingFunction: CSSProperties['transitionTimingFunction'];
-			}
-		| CSSProperties['transition'];
+    animation:
+        | {
+              delay: CSSProperties['animationDelay'];
+              direction: CSSProperties['animationDirection'];
+              duration: CSSProperties['animationDuration'];
+              iterationCount: CSSProperties['animationIterationCount'];
+              name: CSSProperties['animationName'];
+              playState: CSSProperties['animationPlayState'];
+              timingFunction: CSSProperties['animationTimingFunction'];
+          }
+        | CSSProperties['animation'];
+    background:
+        | {
+              attachment: CSSProperties['backgroundAttachment'];
+              color: CSSProperties['backgroundColor'];
+              image: CSSProperties['backgroundImage'];
+              position: CSSProperties['backgroundPosition'] | number[]; // Can be written using array e.g. `[0 0]`
+              repeat: CSSProperties['backgroundRepeat'];
+              size:
+                  | CSSProperties['backgroundSize']
+                  | Array<CSSProperties['backgroundSize']>; // Can be written using array e.g. `['center' 'center']`
+          }
+        | CSSProperties['background'];
+    border:
+        | {
+              color: CSSProperties['borderColor'];
+              style: CSSProperties['borderStyle'];
+              width: CSSProperties['borderWidth'];
+          }
+        | CSSProperties['border'];
+    boxShadow:
+        | {
+              x: Length;
+              y: Length;
+              blur: Length;
+              spread: Length;
+              color: CSSProperties['color'];
+              inset?: 'inset'; // If you want to add inset you need to write 'inset: 'inset''
+          }
+        | CSSProperties['boxShadow'];
+    flex:
+        | {
+              basis: CSSProperties['flexBasis'];
+              direction: CSSProperties['flexDirection'];
+              flow: CSSProperties['flexFlow'];
+              grow: CSSProperties['flexGrow'];
+              shrink: CSSProperties['flexShrink'];
+              wrap: CSSProperties['flexWrap'];
+          }
+        | CSSProperties['flex'];
+    font:
+        | {
+              family: CSSProperties['fontFamily'];
+              size: CSSProperties['fontSize'];
+              stretch: CSSProperties['fontStretch'];
+              style: CSSProperties['fontStyle'];
+              variant: CSSProperties['fontVariant'];
+              weight: CSSProperties['fontWeight'];
+          }
+        | CSSProperties['font'];
+    listStyle:
+        | {
+              image: CSSProperties['listStyleImage'];
+              position: CSSProperties['listStylePosition'];
+              type: CSSProperties['listStyleType'];
+          }
+        | CSSProperties['listStyle'];
+    margin:
+        | {
+              bottom: CSSProperties['marginBottom'];
+              left: CSSProperties['marginLeft'];
+              right: CSSProperties['marginRight'];
+              top: CSSProperties['marginTop'];
+          }
+        | CSSProperties['margin'];
+    padding:
+        | {
+              bottom: CSSProperties['paddingBottom'];
+              left: CSSProperties['paddingLeft'];
+              right: CSSProperties['paddingRight'];
+              top: CSSProperties['paddingTop'];
+          }
+        | CSSProperties['padding'];
+    outline:
+        | {
+              color: CSSProperties['outlineColor'];
+              style: CSSProperties['outlineStyle'];
+              width: CSSProperties['outlineWidth'];
+          }
+        | CSSProperties['outline'];
+    textShadow:
+        | {
+              x: Length;
+              y: Length;
+              blur: Length;
+              color: CSSProperties['color'];
+          }
+        | CSSProperties['textShadow'];
+    transition:
+        | {
+              delay: CSSProperties['transitionDelay'];
+              duration: CSSProperties['transitionDuration'];
+              property: CSSProperties['transitionProperty'];
+              timingFunction: CSSProperties['transitionTimingFunction'];
+          }
+        | CSSProperties['transition'];
 }
 
 export type JssExpandArr = { [k in keyof JssExpand]?: JssExpand[k] | Array<JssExpand[k]> };
 
 export type SimpleStyle = CSSProperties & JssProps & JssExpandArr;
-export type Style = SimpleStyle | Observable<csstype.PropertiesHyphen<string | number>>;
+export type Style = SimpleStyle | Observable<csstype.PropertiesHyphen<Length>>;