Issue #2033211 by jwilson3, LewisNyman, sqndr, tim.plunkett, JamesLefrère | yannickoo: Move Seven CSS files into css directory.

Issue #2230997 by dinarcon, jiv_e, StevenPatz, jstoller, cs_shadow, LewisNyman, lauriii | penyaskito: Fixed Remove the slogan in install.php and update.php.

Revert "Issue #2033211 by LewisNyman, tim.plunkett, JamesLefrère | yannickoo: Move Seven CSS files into css directory."

This reverts commit 16e60c42.

Issue #2033211 by LewisNyman, tim.plunkett, JamesLefrère | yannickoo: Move Seven CSS files into css directory.

Issue #1912610 by amitgoyal, BryanCGreen24, lokapujya, Rajendar Reddy, echoz, barraponto, LewisNyman, pixelwhip: Rename layout classes to follow the layout style naming convention.

Issue #2169765 by philipz, Sutharsan, ckrina, c_lehel, LewisNyman: Redesign update.php to be more consistent with the installation process.

Revert "Issue #2169765 by philipz, Sutharsan, ckrina, c_lehel, LewisNyman: Redesign update.php to be more consistent with the installation process."

This reverts commit 728aad1d.

Issue #2169765 by philipz, Sutharsan, ckrina, c_lehel, LewisNyman: Redesign update.php to be more consistent with the installation process.

Issue #2041793 by mortendk, rteijeiro, LewisNyman, magnify, axe312, zorp, mdrummond: Install-page.html.twig markup and CSS.

Issue #2100509 by emma.maria, dcrocks, csakiistvan, Manjit.Singh: Password strength indicator for site maintenance account is aligned incorrectly on the installation screen.

Issue #2032895 by balsama, yannickoo, corbacho, Kendall Totten: Follow-up use better technique for vertical centering.

Issue #2070785 by thamas: Fixed Password confirm text lolls out from the layout in the install page .

Issue #2030625 by ckrina, emma_maria, mordonez: 'Drupal is already installed' page looks misaligned.

Issue #2015789 by fubhy, echoz, rteijeiro, LewisNyman, penyaskito: Remove language_css_alter() (RTL stylesheets) in favor of HTML 'dir' attribute.

Issue #1337554 by LewisNyman, Bojhan, YesCT, Cottser, jenlampton, Xano, David_Rothstein, larowlan, nilnullvoid: Develop and use separate branding for the installer.