Second attempt to fix CSS regression.

[montehurd]

6.0.5 (#137) fixed the CSS regression when developing locally, but when 6.0.5 was published the CollapseTable css again jumped above the ThemeTransform css. Based on the information below I suspect extract-text-webpack-plugin is at fault.

So this PR uses mini-css-extract-plugin instead of extract-text-webpack-plugin, per the recommendations in the comments linked below.

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How can I keep the css order in the css file when I use extract-text-webpack-plugin？

webpack-contrib/extract-text-webpack-plugin#200

...extract-text-webpack-plugin is for webpack3 and older (will not support webpack 4 it seems). They say to move to mini-css-extract-plugin...

webpack-contrib/extract-text-webpack-plugin#200 (comment)

The webpack >= v4.0.0 'support' for extract-text-webpack-plugin was moved to mini-css-extract-plugin as more lightweight approach for webpack >= v4.0.0 and ETWP entered maintenance mode. We are sorry for the inconvenience here, but ETWP reached a point where maintaining it become too much of a burden and it's not the first time upgrading a major webpack version was complicated and cumbersome due to issues with ETWP. The mid-term plan is integrate CSS support directly into webpack to avoid this kind of issue in the future

webpack-contrib/extract-text-webpack-plugin#701 (comment)

[sharvaniharan]

Looks good on Android

[sharvaniharan]

baseline at the top too