Invalid custom CSS breaks everything

[ibtphil]

When the syntax of custom css is off it completely tubes the admin. Deleting the config entry in the database resets the admin.

Less_Exception_Chunk thrown with message "ParseError: Unexpected input in anonymous-file-0.less on line 4, column 5
2|     color: #ffff00;
3|     text-transform: uppercase;
4|     font-face: Din Alternate,
5|     font-weight: 900;
6| 
7| }"

Stacktrace:
#23 Less_Exception_Chunk in /home/unlikely69/public_html/flarum/vendor/oyejorge/less.php/lib/Less/Parser.php:535
#22 Less_Parser:GetRules in /home/unlikely69/public_html/flarum/vendor/oyejorge/less.php/lib/Less/Parser.php:474
#21 Less_Parser:_parse in /home/unlikely69/public_html/flarum/vendor/oyejorge/less.php/lib/Less/Parser.php:297
#20 Less_Parser:parse in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Assets/LessCompiler.php:31
#19 Flarum\Assets\LessCompiler:compile in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Assets/RevisionCompiler.php:57
#18 Flarum\Assets\RevisionCompiler:getFile in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Assets/AssetManager.php:63
#17 Flarum\Assets\AssetManager:getCssFile in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Support/ClientView.php:264
#16 Flarum\Support\ClientView:render in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Support/HtmlAction.php:28
#15 Flarum\Support\HtmlAction:handle in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Admin/AdminServiceProvider.php:70
#14 Flarum\Admin\AdminServiceProvider:Flarum\Admin\{closure} in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Http/RouterMiddleware.php:65
#13 Flarum\Http\RouterMiddleware:__invoke in <#unknown>:0
#12 call_user_func in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-stratigility/src/Dispatch.php:79
#11 Zend\Stratigility\Dispatch:__invoke in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-stratigility/src/Next.php:111
#10 Zend\Stratigility\Next:__invoke in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Admin/Middleware/LoginWithCookieAndCheckAdmin.php:48
#9 Flarum\Admin\Middleware\LoginWithCookieAndCheckAdmin:__invoke in <#unknown>:0
#8 call_user_func in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-stratigility/src/Dispatch.php:79
#7 Zend\Stratigility\Dispatch:__invoke in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-stratigility/src/Next.php:111
#6 Zend\Stratigility\Next:__invoke in /home/unlikely69/public_html/flarum/vendor/flarum/core/src/Api/Middleware/ReadJsonParameters.php:32
#5 Flarum\Api\Middleware\ReadJsonParameters:__invoke in <#unknown>:0
#4 call_user_func in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-stratigility/src/Dispatch.php:79
#3 Zend\Stratigility\Dispatch:__invoke in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-stratigility/src/Next.php:111
#2 Zend\Stratigility\Next:__invoke in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-stratigility/src/MiddlewarePipe.php:76
#1 Zend\Stratigility\MiddlewarePipe:__invoke in /home/unlikely69/public_html/flarum/vendor/zendframework/zend-diactoros/src/Server.php:166
#0 Zend\Diactoros\Server:listen in /home/unlikely69/public_html/admin.php:46