Issue #3356372 by Gauravvvv, BEGRAFX, smustgrave: Bad Color combination in "Block Layout" Example page

Issue #3343212 by markconroy, andy-blum, bnjmnm, longwave, alexpott, lauriii, codexmas, harsha012, rpayanm, occupant, Mukeysh, leahtard, joelpittet: Update Core CSS to use double-colon for pseudo elements

Issue #2878548 by alexpott, droplet, Cottser, idebr, joelpittet, xjm, martin107: Fix CSS whitespace issues

Issue #2513534 by tim.plunkett, lokapujya, tedbow, LewisNyman, Manjit.Singh, alexpott, Maninders, Bojhan: Remove the 'disabled' region from Block UI

Issue #2567845 by LewisNyman, davidhernandez: [regression] Fix any visual regressions from moving the System CSS to Classy

Issue #2512456 by tim.plunkett, legolasbo, MattA, dawehner, googletorp, darol100, Bojhan, webchick, andypost, ivanstegic, larowlan, lauriii, LewisNyman, tkoleary, rickvug, eliza411, lunk_rat, nickrosencrans, stpaultim, Mark LaCroix: Implement the new block layout design to emphasize the primary interaction of placing a block

Issue #2422399 by aliyakhan, JCL324, mortendk, skippednote, rpayanm, tadityar, LewisNyman, joelpittet, idebr: Rewrite block.admin.css inline with our CSS standards

Issue #2056173 by philipz, Sam152 | tim.plunkett: Regression: Two-column layout is broken by vertical toolbar.

Issue #1662954 by balis_m, mjonesdinero, kalpaitch, IshaDakota, kerasai, ckrina, BarisW | ZenDoodles: Use less-specific tabledrag selectors.

Issue #1956448 by benjy, tim.plunkett, ed.hollinghurst, YesCT: Use the block instance title on the block admin listing.

Issue #1987066 by Kevin Morse, JohnAlbin, rteijeiro, echoz, ry5n: Rename files to match CSS file naming convention.