Accessibility: Plugins: Accessibility and CSS improvements for the Plugins pages.

- improves checkboxes alignment on the "Plugins" page table in the responsive view 
- improves spacing between form controls on the "Add Plugins" page in the responsive view 
- the layout of the "filter bar" on the "Add Plugins" page is now based on CSS Flexbox 
- removes italic type from a paragraph in the "Favorites" page

Props passoniate, garethgillman, maxpertici, audrasjb, sabernhardt, afercia.
See #47327.
Fixes #49231.


git-svn-id: https://develop.svn.wordpress.org/trunk@48281 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/common.css

@@ -1086,8 +1086,24 @@ th.action-links {
 	margin: 0;
 }
 
+/* Use flexbox only on the plugins install page. The `filter-links` and search form children will become flex items. */
+.plugin-install-php .wp-filter {
+	display: flex;
+	flex-wrap: wrap;
+	justify-content: space-between;
+	align-items: center;
+}
+
 .wp-filter .search-form.search-plugins {
+	/* This element is a flex item: the inherited float won't have any effect. */
+	margin-top: 0;
+}
+
+.wp-filter .search-form.search-plugins select,
+.wp-filter .search-form.search-plugins .wp-filter-search {
 	display: inline-block;
+	margin-top: 10px;
+	vertical-align: top;
 }
 
 .wp-filter .button.drawer-toggle {
@@ -3968,6 +3984,11 @@ img {
 	.wp-filter .search-form input[type="search"] {
 		font-size: 1rem;
 	}
+
+	.wp-filter .search-form.search-plugins {
+		/* This element is a flex item. */
+		min-width: 100%;
+	}
 }
 
 /* Smartphone */

src/wp-admin/css/list-tables.css

@@ -2094,6 +2094,16 @@ div.action-links,
 		line-height: 1.5;
 	}
 
+	.plugins tbody th.check-column {
+		padding: 8px 0 0 5px;
+	}
+
+	.plugins thead td.check-column,
+	.plugins tfoot td.check-column,
+	.plugins .inactive th.check-column {
+		padding-left: 9px;
+	}
+
 	/* Add New plugins page */
 	table.plugin-install .column-name,
 	table.plugin-install .column-version,