XF 2.0 How to solve problem: Less_Exception_Compiler

[domfootwear]

Dear All,

Could you show me the way to fix error as below:

Less_Exception_Compiler: variable @primaryLighterStill is undefined in file anonymous-file-0.less in anonymous-file-0.less src/vendor/oyejorge/less.php/lib/Less/Tree/Variable.php:49

Stack Trace
#0 src/vendor/oyejorge/less.php/lib/Less/Tree/Expression.php(52): Less_Tree_Variable->compile(Object(Less_Environment))
#1 src/vendor/oyejorge/less.php/lib/Less/Tree/Value.php(27): Less_Tree_Expression->compile(Object(Less_Environment))
#2 src/vendor/oyejorge/less.php/lib/Less/Tree/Rule.php(75): Less_Tree_Value->compile(Object(Less_Environment))
#3 src/vendor/oyejorge/less.php/lib/Less/Tree/Ruleset.php(94): Less_Tree_Rule->compile(Object(Less_Environment))
#4 src/vendor/oyejorge/less.php/lib/Less/Tree/Ruleset.php(94): Less_Tree_Ruleset->compile(Object(Less_Environment))
#5 src/vendor/oyejorge/less.php/lib/Less/Parser.php(199): Less_Tree_Ruleset->compile(Object(Less_Environment))
#6 src/XF/CssRenderer.php(363): Less_Parser->getCss()
#7 src/XF/CssRenderer.php(311): XF\CssRenderer->renderToCss('public:extra.le...', '// Note that th...')
#8 src/XF/CssRenderer.php(235): XF\CssRenderer->renderTemplate('public:extra.le...', NULL)
#9 src/XF/CssRenderer.php(101): XF\CssRenderer->renderTemplates(Array, Array, Array)
#10 src/XF/CssWriter.php(53): XF\CssRenderer->render(Array)
#11 css.php(30): XF\CssWriter->run(Array, 2, 2, '7ef90d993312114...')
#12 {main}

Request State
array(4) {
  ["url"] => string(211) "/diendan/css.php?css=public%3Aattachments.less%2Cpublic%3Abb_code.less%2Cpublic%3Amessage.less%2Cpublic%3Ashare_controls.less%2Cpublic%3Aextra.less&s=2&l=2&d=1527661906&k=7ef90d99331211452500d8b7c7d28dfb40fb21b2"
  ["referrer"] => string(127) "https://www.giaiphapexcel.com/diendan/threads/c%C3%B4ng-th%E1%BB%A9c-t%C3%ADnh-t%E1%BB%95ng-tr%C3%AAn-nhi%E1%BB%81u-sheet.1179/"
  ["_GET"] => array(5) {
    ["css"] => string(108) "public:attachments.less,public:bb_code.less,public:message.less,public:share_controls.less,public:extra.less"
    ["s"] => string(1) "2"
    ["l"] => string(1) "2"
    ["d"] => string(10) "1527661906"
    ["k"] => string(40) "7ef90d99331211452500d8b7c7d28dfb40fb21b2"
  }
  ["_POST"] => array(0) {
  }
}

Thanks in advance,