Make SideBySide stripe background aligned across lines

"background-attachment: fixed;" seems to distract people when scrolling.

Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

example/diff-table.css

@@ -76,9 +76,9 @@
 .diff-wrapper.diff.diff-html .change.change-eq .new {
   background: #fff;
 }
-.diff-wrapper.diff.diff-html .change.change-ins .old, .diff-wrapper.diff.diff-html .change.change-del .new {
+.diff-wrapper.diff.diff-html .change.change-ins .old, .diff-wrapper.diff.diff-html .change.change-del .new, .diff-wrapper.diff.diff-html .change.change-rep .old:empty, .diff-wrapper.diff.diff-html .change.change-rep .new:empty {
   cursor: not-allowed;
-  background: repeating-linear-gradient(-45deg, #ebebeb, #ebebeb 5px, #e0e0e0 5px, #e0e0e0 10px);
+  background: repeating-linear-gradient(-45deg, whitesmoke, whitesmoke 0.5em, #e8e8e8 0.5em, #e8e8e8 0.9em);
 }
 .diff-wrapper.diff.diff-html .change .old {
   background: #fbe1e1;

example/diff-table.scss

@@ -28,8 +28,8 @@
 
   // color for the nonexistent block
   // for example, there are a deleted line that has no corresponding one
-  $bg-color-nonexistent-block: mix($bg-color, $table-sidebar-color, 60%);
-  $bg-color-nonexistent-block-alternative: mix($bg-color, $table-sidebar-color, 40%);
+  $bg-color-nonexistent-block: mix($bg-color, $table-sidebar-color, 80%);
+  $bg-color-nonexistent-block-alternative: mix($bg-color, $table-sidebar-color, 55%);
 
   background-color: $bg-color;
   border-collapse: collapse;
@@ -120,15 +120,18 @@
       }
 
       &.change-ins .old,
-      &.change-del .new {
+      &.change-del .new,
+      &.change-rep .old:empty,
+      &.change-rep .new:empty {
         cursor: not-allowed;
         background: repeating-linear-gradient(
           -45deg,
           $bg-color-nonexistent-block,
-          $bg-color-nonexistent-block 5px,
-          $bg-color-nonexistent-block-alternative 5px,
-          $bg-color-nonexistent-block-alternative 10px,
+          $bg-color-nonexistent-block 0.5em,
+          $bg-color-nonexistent-block-alternative 0.5em,
+          $bg-color-nonexistent-block-alternative 0.9em,
         );
+        // background-attachment: fixed;
       }
 
       .old {