diff --git a/package-lock.json b/package-lock.json
index 2a9531c..3b01e8d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -5042,6 +5042,12 @@
         "write": "^0.2.1"
       }
     },
+    "flatten": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/flatten/-/flatten-1.0.2.tgz",
+      "integrity": "sha1-2uRqnXj74lKSJYzB54CkHZXAN4I=",
+      "dev": true
+    },
     "flow-bin": {
       "version": "0.77.0",
       "resolved": "https://registry.npmjs.org/flow-bin/-/flow-bin-0.77.0.tgz",
@@ -5538,12 +5544,14 @@
         "balanced-match": {
           "version": "1.0.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "brace-expansion": {
           "version": "1.1.11",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "balanced-match": "^1.0.0",
             "concat-map": "0.0.1"
@@ -5558,17 +5566,20 @@
         "code-point-at": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "concat-map": {
           "version": "0.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "console-control-strings": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "core-util-is": {
           "version": "1.0.2",
@@ -5685,7 +5696,8 @@
         "inherits": {
           "version": "2.0.3",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "ini": {
           "version": "1.3.5",
@@ -5697,6 +5709,7 @@
           "version": "1.0.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "number-is-nan": "^1.0.0"
           }
@@ -5711,6 +5724,7 @@
           "version": "3.0.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "brace-expansion": "^1.1.7"
           }
@@ -5718,12 +5732,14 @@
         "minimist": {
           "version": "0.0.8",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "minipass": {
           "version": "2.2.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "safe-buffer": "^5.1.1",
             "yallist": "^3.0.0"
@@ -5742,6 +5758,7 @@
           "version": "0.5.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "minimist": "0.0.8"
           }
@@ -5822,7 +5839,8 @@
         "number-is-nan": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "object-assign": {
           "version": "4.1.1",
@@ -5834,6 +5852,7 @@
           "version": "1.4.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "wrappy": "1"
           }
@@ -5955,6 +5974,7 @@
           "version": "1.0.2",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "code-point-at": "^1.0.0",
             "is-fullwidth-code-point": "^1.0.0",
@@ -7969,6 +7989,7 @@
           "version": "0.1.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "kind-of": "^3.0.2",
             "longest": "^1.0.1",
@@ -8952,7 +8973,8 @@
         "longest": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "lru-cache": {
           "version": "4.1.3",
@@ -10990,20 +11012,46 @@
       }
     },
     "postcss-custom-properties": {
-      "version": "7.0.0",
-      "resolved": "https://registry.npmjs.org/postcss-custom-properties/-/postcss-custom-properties-7.0.0.tgz",
-      "integrity": "sha512-dl/CNaM6z2RBa0vZZqsV6Hunj4HD6Spu7FcAkiVp5B2tgm6xReKKYzI7x7QNx3wTMBNj5v+ylfVcQGMW4xdkHw==",
+      "version": "8.0.0",
+      "resolved": "https://registry.npmjs.org/postcss-custom-properties/-/postcss-custom-properties-8.0.0.tgz",
+      "integrity": "sha512-CfQVcJ7AZHJ3ldRp1Dyk+tb9JW5siQtlhw3H/a5ZbkObv03aaj/KOs0ejAADgrNQGB8tjNwVYxlSa0/dIRAoQg==",
       "dev": true,
       "requires": {
-        "balanced-match": "^1.0.0",
-        "postcss": "^6.0.18"
+        "postcss": "^7.0.2",
+        "postcss-values-parser": "^1.5.0"
       },
       "dependencies": {
-        "balanced-match": {
-          "version": "1.0.0",
-          "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-1.0.0.tgz",
-          "integrity": "sha1-ibTRmasr7kneFk6gK4nORi1xt2c=",
+        "has-flag": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-3.0.0.tgz",
+          "integrity": "sha1-tdRU3CGZriJWmfNGfloH87lVuv0=",
+          "dev": true
+        },
+        "postcss": {
+          "version": "7.0.2",
+          "resolved": "https://registry.npmjs.org/postcss/-/postcss-7.0.2.tgz",
+          "integrity": "sha512-fmaUY5370keLUTx+CnwRxtGiuFTcNBLQBqr1oE3WZ/euIYmGAo0OAgOhVJ3ByDnVmOR3PK+0V9VebzfjRIUcqw==",
+          "dev": true,
+          "requires": {
+            "chalk": "^2.4.1",
+            "source-map": "^0.6.1",
+            "supports-color": "^5.4.0"
+          }
+        },
+        "source-map": {
+          "version": "0.6.1",
+          "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
+          "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
           "dev": true
+        },
+        "supports-color": {
+          "version": "5.5.0",
+          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.5.0.tgz",
+          "integrity": "sha512-QjVjwdXIt408MIiAqCX4oUKsgU2EqAGzs2Ppkm4aQYbjm+ZEWEcW4SfFNTr4uMNZma0ey4f5lgLrkB0aX0QMow==",
+          "dev": true,
+          "requires": {
+            "has-flag": "^3.0.0"
+          }
         }
       }
     },
@@ -11363,6 +11411,17 @@
       "integrity": "sha1-h/OPnxj3dKSrTIojL1xc6IcqnRU=",
       "dev": true
     },
+    "postcss-values-parser": {
+      "version": "1.5.0",
+      "resolved": "https://registry.npmjs.org/postcss-values-parser/-/postcss-values-parser-1.5.0.tgz",
+      "integrity": "sha512-3M3p+2gMp0AH3da530TlX8kiO1nxdTnc3C6vr8dMxRLIlh8UYkz0/wcwptSXjhtx2Fr0TySI7a+BHDQ8NL7LaQ==",
+      "dev": true,
+      "requires": {
+        "flatten": "^1.0.2",
+        "indexes-of": "^1.0.1",
+        "uniq": "^1.0.1"
+      }
+    },
     "prelude-ls": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/prelude-ls/-/prelude-ls-1.1.2.tgz",
diff --git a/package.json b/package.json
index 4103a2c..5a176ce 100644
--- a/package.json
+++ b/package.json
@@ -62,7 +62,7 @@
     "nyc": "^12.0.2",
     "postcss-at-rules-variables": "^0.1.5",
     "postcss-cli": "^6.0.0",
-    "postcss-custom-properties": "^7.0.0",
+    "postcss-custom-properties": "^8.0.0",
     "postcss-discard-comments": "^4.0.0",
     "postcss-each": "^0.10.0",
     "prettier": "^1.13.7",