Standardize the look of new Yeoman-generated SPFx web parts
Creating a web part using the Yeoman generator should produce a web part that is visually indistinguishable from an out-of-the-box SharePoint web part. It should encourage new developers to adopt the UI Fabric look without requiring additional efforts on their part.
On newly created web parts using the SPFx, the CSS styles are inconsistent with the first-party web parts.
For example, the .container CSS class defines box-shadow: 0 2px 4px 0 rgba(0, 0, 0, 0.2), 0 25px 50px 0 rgba(0, 0, 0, 0.1); and max-width: 700px;
None of the other out-of-the-box web parts define a shadow or a max width.
This makes any new web parts look and behave differently than out-of-the-box web parts.
At the very least, I recommend changing the .container CSS class as follows:
margin: 0px auto;