fix: Fix the split in HTML at 33/67% instead of calculating percentages (#939)

Previously this was calculated so that the left page would expand to its natural size. That's not
really what we want, because the natural size could be as high as 100%.

Fixes #927

Author: tmcw

src/default_theme/assets/site.js

@@ -113,15 +113,6 @@ split_left.style.overflow = 'hidden';
 var cw_without_sb = split_left.clientWidth;
 split_left.style.overflow = '';
 
-// Need to add:
-// - Half of gutterSize (i.e. 10) because gutter will take that much from each.
-// - Scrollbar width (cw_with_sb - cw_without_sb), if it takes up existing
-//   space (Firefox) rather than adding the scrollbar to the side (Chrome)
-var percent_left =
-  (split_left.getBoundingClientRect().width + 10 + cw_without_sb - cw_with_sb) /
-  split_parent.getBoundingClientRect().width *
-  100;
-
 Split(['#split-left', '#split-right'], {
   elementStyle: function(dimension, size, gutterSize) {
     return {
@@ -134,7 +125,7 @@ Split(['#split-left', '#split-right'], {
     };
   },
   gutterSize: 20,
-  sizes: [percent_left, 100 - percent_left]
+  sizes: [33, 67]
 });
 
 // Chrome doesn't remember scroll position properly so do it ourselves.