light.msstyles: Use #fefefe instead of #ffffff for scrollbar parts.

Fix Imperium: Greek Wars (1183470) launcher scrollbar largely drawn as transparent.

The application sets a hardcoded #ffffff as the color key for transparency. On Windows, the
scrollbar parts only have very few #ffffff pixels so the scrollbar is drawn as basically opaque.
If a theme that have many 0xffffff pixels is being used, then the bug reproduces as well on Windows.
I don't want to change the light theme style for this. So let's work around this by using #fefefe
instead of #ffffff. This have little difference visually.

Based on investigation done by Santino Mazza.

dlls/light.msstyles/blue_scrollbar_arrows.svg

@@ -8,9 +8,9 @@
    </cc:Work>
   </rdf:RDF>
  </metadata>
- <rect x="-1.875e-5" width="4.4979" height="89.959" fill="#fff"/>
+ <rect x="-1.875e-5" width="4.4979" height="89.959" fill="#fefefe"/>
  <g stroke-width=".26458">
-  <g fill="#fff">
+  <g fill="#fefefe">
    <rect x=".13229" y=".13229" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#aeaeae"/>
    <g stroke="#3096fa">
     <rect x=".13229" y="4.6302" width="4.2334" height="4.2333" rx=".52917" ry=".52917"/>
@@ -21,24 +21,24 @@
    </g>
   </g>
   <rect x=".13229" y="9.1281" width="4.2333" height="4.2333" rx=".52917" ry=".52917" fill="#2979ff" stroke="#2979ff"/>
-  <g fill="#fff">
+  <g fill="#fefefe">
    <rect x=".13229" y="13.626" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#aeaeae"/>
    <rect x=".13229" y="18.124" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#aeaeae"/>
    <rect x=".13229" y="22.622" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#3096fa"/>
   </g>
   <rect x=".13229" y="27.12" width="4.2333" height="4.2333" rx=".52917" ry=".52917" fill="#2979ff" stroke="#2979ff"/>
-  <g fill="#fff">
+  <g fill="#fefefe">
    <rect x=".13229" y="31.618" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#aeaeae"/>
    <rect x=".13229" y="36.116" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#aeaeae"/>
    <rect x=".13229" y="40.614" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#3096fa"/>
   </g>
   <rect x=".13229" y="45.111" width="4.2333" height="4.2333" rx=".52917" ry=".52917" fill="#2979ff" stroke="#2979ff"/>
-  <g fill="#fff">
+  <g fill="#fefefe">
    <rect x=".13229" y="49.609" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#aeaeae"/>
    <rect x=".13229" y="54.107" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#aeaeae"/>
    <rect x=".13229" y="58.605" width="4.2333" height="4.2333" rx=".52917" ry=".52917" stroke="#3096fa"/>
   </g>
   <rect x=".13229" y="63.103" width="4.2333" height="4.2333" rx=".52917" ry=".52917" fill="#2979ff" stroke="#2979ff"/>
-  <rect x=".13229" y="67.601" width="4.2333" height="4.2333" rx=".52917" ry=".52917" fill="#fff" stroke="#aeaeae"/>
+  <rect x=".13229" y="67.601" width="4.2333" height="4.2333" rx=".52917" ry=".52917" fill="#fefefe" stroke="#aeaeae"/>
  </g>
 </svg>

dlls/light.msstyles/blue_scrollbar_thumb_horizontal.svg

@@ -8,8 +8,8 @@
    </cc:Work>
   </rdf:RDF>
  </metadata>
- <g fill="#fff">
-  <rect x="-7.0588e-5" width="5.2918" height="22.49" fill="#fff" stroke-width=".070005"/>
+ <g fill="#fefefe">
+  <rect x="-7.0588e-5" width="5.2918" height="22.49" fill="#fefefe" stroke-width=".070005"/>
   <g stroke-width=".26458">
    <rect x=".13229" y=".13229" width="5.0272" height="4.2333" rx=".52918" ry=".52918" stroke="#aeaeae"/>
    <rect x=".13229" y="4.6302" width="5.0272" height="4.2333" rx=".52918" ry=".52918" stroke="#3096fa"/>

dlls/light.msstyles/blue_scrollbar_thumb_vertical.svg

@@ -8,8 +8,8 @@
    </cc:Work>
   </rdf:RDF>
  </metadata>
- <rect y="-.00012353" width="4.4979" height="14.552" fill="#fff" stroke-width=".26458"/>
- <g fill="#fff" stroke-width=".26458">
+ <rect y="-.00012353" width="4.4979" height="14.552" fill="#fefefe" stroke-width=".26458"/>
+ <g fill="#fefefe" stroke-width=".26458">
   <rect transform="rotate(90)" x=".13229" y="-4.3656" width="2.6458" height="4.2333" rx=".52916" ry=".52916" stroke="#aeaeae"/>
   <rect transform="rotate(90)" x="3.0426" y="-4.3656" width="2.6458" height="4.2333" rx=".52916" ry=".52916" stroke="#3096fa"/>
   <rect transform="rotate(90)" x="11.774" y="-4.3656" width="2.6458" height="4.2333" rx=".52916" ry=".52916" stroke="#3096fa"/>

dlls/uxtheme/tests/system.c

@@ -2699,7 +2699,6 @@ static void test_theme(BOOL v6)
 
     white_percent = white_count * 100 / (scrollbar_width * scrollbar_height);
     if (v6)
-        todo_wine
         ok(white_percent < 4, "Expected #ffffff pixels less than 4%%.\n");
     else
         ok(white_percent < 50, "Expected #ffffff pixels less than 50%%.\n");