update elements and fix some bugs

lib/src/prism/components/prism-scss.js

 Prism.languages.scss = Prism.languages.extend('css', {
         'comment': {
-                pattern: /(^|[^\\])(\/\*[\w\W]*?\*\/|\/\/.*?(\r?\n|$))/,
+                pattern: /(^|[^\\])(?:\/\*[\w\W]*?\*\/|\/\/.*)/,
                 lookbehind: true
         },
         'atrule': {
-                pattern: /@[\w-]+(?:\([^()]+\)|[^(])*?(?=\s+(\{|;))/i,
+                pattern: /@[\w-]+(?:\([^()]+\)|[^(])*?(?=\s+[{;])/,
                 inside: {
                         'rule': /@[\w-]+/
                         // See rest below
                 }
         },
         // url, compassified
-        'url': /([-a-z]+-)*url(?=\()/i,
+        'url': /(?:[-a-z]+-)*url(?=\()/i,
         // CSS selector regex is not appropriate for Sass
         // since there can be lot more things (var, @ directive, nesting..)
         // a selector must start at the end of a property or after a brace (end of other rules or nesting)
-        // it can contain some caracters that aren't used for defining rules or end of selector, & (parent selector), or interpolated variable
+        // it can contain some characters that aren't used for defining rules or end of selector, & (parent selector), or interpolated variable
         // the end of a selector is found when there is no rules in it ( {} or {\s}) or if there is a property (because an interpolated var
         // can "pass" as a selector- e.g: proper#{$erty})
-        // this one was ard to do, so please be careful if you edit this one :)
+        // this one was hard to do, so please be careful if you edit this one :)
         'selector': {
-                pattern: /([^@;\{\}\(\)]?([^@;\{\}\(\)]|&|#\{\$[-_\w]+\})+)(?=\s*\{(\}|\s|[^\}]+(:|\{)[^\}]+))/m,
+                // Initial look-ahead is used to prevent matching of blank selectors
+                pattern: /(?=\S)[^@;\{\}\(\)]?([^@;\{\}\(\)]|&|#\{\$[-_\w]+\})+(?=\s*\{(\}|\s|[^\}]+(:|\{)[^\}]+))/m,
                 inside: {
-                        'placeholder': /%[-_\w]+/i
+                        'placeholder': /%[-_\w]+/
                 }
         }
 });
 
 Prism.languages.insertBefore('scss', 'atrule', {
-        'keyword': /@(if|else if|else|for|each|while|import|extend|debug|warn|mixin|include|function|return|content)|(?=@for\s+\$[-_\w]+\s)+from/i
+        'keyword': [
+                /@(?:if|else(?: if)?|for|each|while|import|extend|debug|warn|mixin|include|function|return|content)/i,
+                {
+                        pattern: /( +)(?:from|through)(?= )/,
+                        lookbehind: true
+                }
+        ]
 });
 
 Prism.languages.insertBefore('scss', 'property', {
         // var and interpolated vars
-        'variable': /((\$[-_\w]+)|(#\{\$[-_\w]+\}))/i
+        'variable': /\$[-_\w]+|#\{\$[-_\w]+\}/
 });
 
 Prism.languages.insertBefore('scss', 'function', {
         'placeholder': {
-                pattern: /%[-_\w]+/i,
+                pattern: /%[-_\w]+/,
                 alias: 'selector'
         },
-        'statement': /\B!(default|optional)\b/i,
-        'boolean': /\b(true|false)\b/,
-        'null': /\b(null)\b/,
-        'operator': /\s+([-+]{1,2}|={1,2}|!=|\|?\||\?|\*|\/|%)\s+/
+        'statement': /\B!(?:default|optional)\b/i,
+        'boolean': /\b(?:true|false)\b/,
+        'null': /\bnull\b/,
+        'operator': {
+                pattern: /(\s)(?:[-+*\/%]|[=!]=|<=?|>=?|and|or|not)(?=\s)/,
+                lookbehind: true
+        }
 });
 
 Prism.languages.scss['atrule'].inside.rest = Prism.util.clone(Prism.languages.scss);