fix: Disallow borders on plot container

[camdecoster]

Description

Disallow borders in plot container in CSS reset.

Changes

• Add borders of zero to CSS reset for plot container

Demo video or screenshots

Before	After

Testing

• Be on this branch
• Edit devtools/test_dashboard/style.css to include the following CSS:

  div {
    border: 1px red solid;
  }

• Load a mock in Plotly DevTools
• Note that the plot container has lots of red borders.
• The changes from this PR need to be compiled to see the changes. Run npm run preprocess to compile the CSS.
• Load a mock in Plotly DevTools
• Note that the plot container has no red borders