Playground: Visualization tab background scrolls with large graphs

[dnlbauer]

In the Visualization tab of the JSON-LD Playground, when the RDF graph becomes large enough to require horizontal scrolling, the white background scrolls with the graph content. As a result, there is a not very appealing transition from the white background to no background at all (see screenshot).

Proposed solution:

The reason for this is that the white background is currently applied to the div container hosting the svg drawn by the jsonld library. If the background style is applied to the svg instead, the content would look as expected:

<div id="pane-visualized" class="tab-pane active">
  <div id="visualized" style="background: white">
    <svg width="1500" height="600">
      <g transform="translate(250,0)">
....

vs.

<div id="pane-visualized" class="tab-pane active">
  <div id="visualized">
    <svg width="1500" height="600" style="background: white">
      <g transform="translate(250,0)">
....