[ui] Op / asset graph node styling polish

[bengotow]

Summary & Motivation

• The shadow of asset nodes is larger than the box they're clipped into so you can see the edge of the shadow. I made the shadow a (non-standard) smaller one

• The "stacked box" of dynamic ops still had the old border radius

• The gray description box of op nodes has a border radius that is too large and there's a sliver of whitespace between it and the outer border (bottom left of box). This should be 6px since it's inside something with an 8px radius + 2px width. (Added a comment to this since we might change it again)

• The op graph boxes used to have a hard left edge with no border radius where they touched their inputs / outputs. They're rounded now, which looks nice, but the IO boxes still had hard edges. I made it so these are always rounded unless there is more than one, in which case the middle ones are joined.

(New version below)

• The asset nodes in legacy mode had an olive border - talked with Josh and changed it to blue200:

How I Tested These Changes

Just tested these visually in experimental light + dark modes

[github-actions]

Deploy preview for dagit-core-storybook ready!

✅ Preview
https://dagit-core-storybook-48adfe17i-elementl.vercel.app
https://bengotow-nits-asset-graph.core-storybook.dagster-docs.io

Built with commit c3ac402.
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[github-actions]

Deploy preview for dagit-storybook ready!

✅ Preview
https://dagit-storybook-h9mg5tglm-elementl.vercel.app
https://bengotow-nits-asset-graph.components-storybook.dagster-docs.io

Built with commit c3ac402.
This pull request is being automatically deployed with vercel-action