将问题与MVC和css变量捆绑在一起

在开发MVC5项目时，我已经在VS2019上安装了。 我正在努力捆绑和缩小来自Uikit的css和JS。Uikit作为引导4使用css变量，例如：

--uk-breakpoint-s:640px;
--uk-breakpoint-l:1200px;
{--uk-leader-fill-content:.}
var(--uk-animation-stroke)
...

在VS2019中，我能够使用Bundler&Minifier工具生成.min。但当我构建或发布我的网站时，我会不断进入浏览器：

/* Minification failed. Returning unminified contents.
(2,3497): run-time error CSS1062: Expected semicolon or closing curly-brace, found '-'
(2,3521): run-time error CSS1062: Expected semicolon or closing curly-brace, found '-'
(2,3545): run-time error CSS1062: Expected semicolon or closing curly-brace, found '-'
(2,3570): run-time error CSS1062: Expected semicolon or closing curly-brace, found '-'
(2,64598): run-time error CSS1062: Expected semicolon or closing curly-brace, found '-'
(2,69161): run-time error CSS1039: Token not allowed after unary operator: '-uk-animation-stroke'
(2,71528): run-time error CSS1039: Token not allowed after unary operator: '-uk-animation-stroke'

这意味着绑定器显然不处理css变量。我读了很多书，它看起来像Bundler&Minifier工具，那么为什么我的浏览器让我返回这个“缩小失败”错误呢