diff --git a/themes/tiddlywiki/vanilla/ThemeTweaks.tid b/themes/tiddlywiki/vanilla/ThemeTweaks.tid
index 30a58f23c..ef56b935a 100644
--- a/themes/tiddlywiki/vanilla/ThemeTweaks.tid
+++ b/themes/tiddlywiki/vanilla/ThemeTweaks.tid
@@ -30,6 +30,14 @@ caption: Theme Tweaks
 </$select>
 \end
 
+\define backgroundimagesize-dropdown()
+<$select tiddler="$:/themes/tiddlywiki/vanilla/settings/backgroundimagesize" default="scroll">
+<option value="auto">Auto</option>
+<option value="cover">Cover</option>
+<option value="contain">Contain</option>
+</$select>
+\end
+
 You can tweak certain aspects of the ''Vanilla'' theme.
 
 ! Options
@@ -42,6 +50,7 @@ You can tweak certain aspects of the ''Vanilla'' theme.
 |[[Code font family|$:/themes/tiddlywiki/vanilla/settings/codefontfamily]] |<$edit-text tiddler="$:/themes/tiddlywiki/vanilla/settings/codefontfamily" default="" tag="input"/> | |
 |[[Page background image|$:/themes/tiddlywiki/vanilla/settings/backgroundimage]] |<$edit-text tiddler="$:/themes/tiddlywiki/vanilla/settings/backgroundimage" default="" tag="input"/> |<<backgroundimage-dropdown>> |
 |[[Page background image attachment |$:/themes/tiddlywiki/vanilla/settings/backgroundimageattachment]] |<<backgroundimageattachment-dropdown>> | |
+|[[Page background image size |$:/themes/tiddlywiki/vanilla/settings/backgroundimagesize]] |<<backgroundimagesize-dropdown>> | |
 
 ! Sizes
 
diff --git a/themes/tiddlywiki/vanilla/base.tid b/themes/tiddlywiki/vanilla/base.tid
index e1f67848d..4f95f88f4 100644
--- a/themes/tiddlywiki/vanilla/base.tid
+++ b/themes/tiddlywiki/vanilla/base.tid
@@ -2,19 +2,23 @@ title: $:/themes/tiddlywiki/vanilla/base
 tags: [[$:/tags/Stylesheet]]
 
 \define custom-background-datauri()
-<$reveal state="$:/themes/tiddlywiki/vanilla/settings/backgroundimage" type="nomatch" text="">
 <$set name="background" value={{$:/themes/tiddlywiki/vanilla/settings/backgroundimage}}>
 <$list filter="[<background>is[image]]">
+`background: url(`
 <$list filter="[<background>!has[_canonical_uri]]">
-`background: url(`<$macrocall $name="datauri" title={{$:/themes/tiddlywiki/vanilla/settings/backgroundimage}}/>`);`
+<$macrocall $name="datauri" title={{$:/themes/tiddlywiki/vanilla/settings/backgroundimage}}/>
 </$list>
 <$list filter="[<background>has[_canonical_uri]]">
-`background: url(`<$view tiddler={{$:/themes/tiddlywiki/vanilla/settings/backgroundimage}} field="_canonical_uri"/>`);`
+<$view tiddler={{$:/themes/tiddlywiki/vanilla/settings/backgroundimage}} field="_canonical_uri"/>
 </$list>
-`background-attachment: `{{$:/themes/tiddlywiki/vanilla/settings/backgroundimageattachment}}`;`
+`);`
+`background-attachment: `{{$:/themes/tiddlywiki/vanilla/settings/backgroundimageattachment}}`;
+-webkit-background-size:` {{$:/themes/tiddlywiki/vanilla/settings/backgroundimagesize}}`;
+-moz-background-size:` {{$:/themes/tiddlywiki/vanilla/settings/backgroundimagesize}}`;
+-o-background-size:` {{$:/themes/tiddlywiki/vanilla/settings/backgroundimagesize}}`;
+background-size:` {{$:/themes/tiddlywiki/vanilla/settings/backgroundimagesize}}`;`
 </$list>
 </$set>
-</$reveal>
 \end
 
 \rules only filteredtranscludeinline transcludeinline macrodef macrocallinline