MM-37809 Theming tweaks (#26289)

* tweaked dark themes and quartz theme

* refinements to themes

* tweaked denim global header color

* updates to quartz and sapphire themes

* tweaked quartz theme

* tweaks to indigo theme

* minor tweaks to themes

* update snapshots

* updated hex colors to consistent casing and updated snapshots

webapp/channels/src/components/user_settings/display/user_settings_theme/custom_theme_chooser/__snapshots__/custom_theme_chooser.test.tsx.snap

@@ -91,7 +91,7 @@ exports[`components/user_settings/display/CustomThemeChooser should match, init
             />
           }
           onChange={[Function]}
-          value="#14213e"
+          value="#162545"
         />
       </div>
       <div
@@ -559,7 +559,7 @@ exports[`components/user_settings/display/CustomThemeChooser should match, init
         onClick={[Function]}
         onCopy={[Function]}
         onPaste={[Function]}
-        value="{\\"sidebarBg\\":\\"#1e325c\\",\\"sidebarText\\":\\"#ffffff\\",\\"sidebarUnreadText\\":\\"#ffffff\\",\\"sidebarTextHoverBg\\":\\"#28427b\\",\\"sidebarTextActiveBorder\\":\\"#5d89ea\\",\\"sidebarTextActiveColor\\":\\"#ffffff\\",\\"sidebarHeaderBg\\":\\"#192a4d\\",\\"sidebarHeaderTextColor\\":\\"#ffffff\\",\\"sidebarTeamBarBg\\":\\"#14213e\\",\\"onlineIndicator\\":\\"#3db887\\",\\"awayIndicator\\":\\"#ffbc1f\\",\\"dndIndicator\\":\\"#d24b4e\\",\\"mentionBg\\":\\"#ffffff\\",\\"mentionBj\\":\\"#ffffff\\",\\"mentionColor\\":\\"#1e325c\\",\\"centerChannelBg\\":\\"#ffffff\\",\\"centerChannelColor\\":\\"#3f4350\\",\\"newMessageSeparator\\":\\"#cc8f00\\",\\"linkColor\\":\\"#386fe5\\",\\"buttonBg\\":\\"#1c58d9\\",\\"buttonColor\\":\\"#ffffff\\",\\"errorTextColor\\":\\"#d24b4e\\",\\"mentionHighlightBg\\":\\"#ffd470\\",\\"mentionHighlightLink\\":\\"#1b1d22\\",\\"codeTheme\\":\\"github\\"}"
+        value="{\\"sidebarBg\\":\\"#1e325c\\",\\"sidebarText\\":\\"#ffffff\\",\\"sidebarUnreadText\\":\\"#ffffff\\",\\"sidebarTextHoverBg\\":\\"#28427b\\",\\"sidebarTextActiveBorder\\":\\"#5d89ea\\",\\"sidebarTextActiveColor\\":\\"#ffffff\\",\\"sidebarHeaderBg\\":\\"#192a4d\\",\\"sidebarHeaderTextColor\\":\\"#ffffff\\",\\"sidebarTeamBarBg\\":\\"#162545\\",\\"onlineIndicator\\":\\"#3db887\\",\\"awayIndicator\\":\\"#ffbc1f\\",\\"dndIndicator\\":\\"#d24b4e\\",\\"mentionBg\\":\\"#ffffff\\",\\"mentionBj\\":\\"#ffffff\\",\\"mentionColor\\":\\"#1e325c\\",\\"centerChannelBg\\":\\"#ffffff\\",\\"centerChannelColor\\":\\"#3f4350\\",\\"newMessageSeparator\\":\\"#cc8f00\\",\\"linkColor\\":\\"#386fe5\\",\\"buttonBg\\":\\"#1c58d9\\",\\"buttonColor\\":\\"#ffffff\\",\\"errorTextColor\\":\\"#d24b4e\\",\\"mentionHighlightBg\\":\\"#ffd470\\",\\"mentionHighlightLink\\":\\"#1b1d22\\",\\"codeTheme\\":\\"github\\"}"
       />
       <div
         className="mt-3"