Add minifyStyles plugin, test and dependencies.

.svgo.yml

@@ -22,6 +22,7 @@ plugins:
   - removeMetadata
   - removeEditorsNSData
   - cleanupAttrs
+  - minifyStyles
   - convertStyleToAttrs
   - cleanupIDs
   - removeRasterImages

package.json

@@ -44,7 +44,8 @@
     "js-yaml": "~3.3.1",
     "colors": "~1.1.2",
     "whet.extend": "~0.9.9",
-    "mkdirp": "~0.5.1"
+    "mkdirp": "~0.5.1",
+    "csso": "~1.4.1"
   },
   "devDependencies": {
     "mocha": "~2.2.5",

plugins/minifyStyles.js

@@ -0,0 +1,71 @@
+'use strict';
+
+exports.type = 'perItem';
+
+exports.active = true;
+
+exports.params = {
+  svgo: {}
+};
+
+exports.description = 'minifies existing styles in svg';
+
+var csso = require('csso');
+
+
+// wraps css rules into a selector to make it parseable
+var rulesToDummySelector = function(str) {
+    return '.dummy { ' + str + ' }';
+};
+
+// helper to extract css rules from full css selector
+var extractRuleCss = function(str) {
+    var strEx = str.match(/\.dummy{(.*)}/i)[1];
+    return strEx;
+};
+
+// minifies css using csso
+var minifyCss = function(css, options) {
+  return csso.minify(css);
+};
+
+
+
+/**
+  * Minifies styles (<style> element + style attribute) using svgo
+  *
+  * @param {Object} item current iteration item
+  * @return {Boolean} if false, item will be filtered out
+  *
+  * @author strarsis <strarsis@gmail.com>
+  */
+exports.fn = function(item, svgoOptions) {
+
+        if(item.elem) {
+          if(item.isElem('style')) {
+            var styleCss = item.content[0].text;
+            if(styleCss.length > 0) {
+              var styleCssMinified = minifyCss(styleCss, svgoOptions);
+              item.content[0].text = styleCssMinified;
+            }
+          }
+
+          if(item.hasAttr('style')) {
+            var itemCss = item.attr('style').value;
+            if(itemCss.length > 0) {
+              var itemCssMinified =
+                extractRuleCss(
+                  minifyCss(
+                    rulesToDummySelector(
+                      itemCss
+                    ),
+                    svgoOptions
+                  )
+                );
+              item.attr('style').value = itemCssMinified;
+            }
+          }
+        }
+
+        return item;
+};

test/plugins/minifyStyles.01.svg

@@ -0,0 +1,15 @@
+<svg id="test" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
+    <style>
+        .st0{ fill:red; padding-top: 1em; padding-right: 1em; padding-bottom: 1em; padding-left: 1em; } @media screen and (max-width: 200px) { .st1 { display: none; } }
+    </style>
+    <rect width="100" height="100" class="st0" style="stroke-width:3; margin-top: 1em; margin-right: 1em; margin-bottom: 1em; margin-left: 1em;"/>
+</svg>
+
+@@@
+
+<svg id="test" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
+    <style>
+        .st0{fill:red;padding:1em}@media screen and (max-width:200px){.st1{display:none}}
+    </style>
+    <rect width="100" height="100" class="st0" style="stroke-width:3;margin:1em"/>
+</svg>