Remove transparent border-top from Elements tree rows
Remove transparent border-top from Elements tree rows

Previously, Elements tree rows had a transparent border-top to fix a bug
where there was unclick-able deadspace in between rows. This patch
removes the transparent border-top in favor of padding-top, since the
`forced-colors` heuristic makes these borders visible in high-contrast
mode.

Before: https://i.imgur.com/AEb8sSM.png
After: https://i.imgur.com/MAqFaxf.png
Bug: 1048378
Change-Id: I5c077d344f18d5b3f81419562ed030f5d0f8a9fc
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2076623
Reviewed-by: Mathias Bynens <17a2cbc4e33156874a9862b0f530521117e66a3d@chromium.org>
Commit-Queue: Kalon Hinds <0953a07de5dd99912b5643571c8ed9864c017a6d@microsoft.com>

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