fix(reader): set background-color on html/body instead of background: none

background: none on html/body exposed the iframe's default black
background in gaps around the content. Now uses background-color
matching the theme color, and stops forcing background on body *
which caused black bars around page margins.

web/src/reader/reader.ts

@@ -269,12 +269,11 @@ const getCSS = ({
     ${fontFamilyRule}
     html, body {
         color: ${theme.fg} !important;
-        background: none !important;
+        background-color: ${theme.bg} !important;
     }
     body * {
         color: inherit !important;
         border-color: currentColor !important;
-        background-color: ${theme.bg} !important;
     }
     a:any-link {
         color: ${theme.link} !important;