diff --git a/src/components/App.jsx b/src/components/App.jsx
index 9463229..839129d 100644
--- a/src/components/App.jsx
+++ b/src/components/App.jsx
@@ -393,8 +393,7 @@ export default class App extends React.Component {
   }
 
   onUndo = () => {
-    let activeStyle;
-    activeStyle = this.revisionStore.undo()
+    const activeStyle = this.revisionStore.undo()
 
     const messages = undoMessages(this.state.mapStyle, activeStyle)
     this.onStyleChanged(activeStyle, {addRevision: false});
diff --git a/src/components/fields/_FunctionButtons.jsx b/src/components/fields/_FunctionButtons.jsx
index 674f55e..e96b135 100644
--- a/src/components/fields/_FunctionButtons.jsx
+++ b/src/components/fields/_FunctionButtons.jsx
@@ -3,6 +3,7 @@ import PropTypes from 'prop-types'
 
 import Button from '../Button'
 import {MdFunctions, MdInsertChart} from 'react-icons/md'
+import {mdiFunctionVariant} from '@mdi/js';
 
 
 /**
@@ -41,7 +42,7 @@ export default class FunctionButtons extends React.Component {
           onClick={this.props.onExpressionClick}
         >
           <svg style={{width:"14px", height:"14px", verticalAlign: "middle"}} viewBox="0 0 24 24">
-            <path fill="currentColor" d="M12.42,5.29C11.32,5.19 10.35,6 10.25,7.11L10,10H12.82V12H9.82L9.38,17.07C9.18,19.27 7.24,20.9 5.04,20.7C3.79,20.59 2.66,19.9 2,18.83L3.5,17.33C3.83,18.38 4.96,18.97 6,18.63C6.78,18.39 7.33,17.7 7.4,16.89L7.82,12H4.82V10H8L8.27,6.93C8.46,4.73 10.39,3.1 12.6,3.28C13.86,3.39 15,4.09 15.66,5.17L14.16,6.67C13.91,5.9 13.23,5.36 12.42,5.29M22,13.65L20.59,12.24L17.76,15.07L14.93,12.24L13.5,13.65L16.35,16.5L13.5,19.31L14.93,20.72L17.76,17.89L20.59,20.72L22,19.31L19.17,16.5L22,13.65Z" />
+            <path fill="currentColor" d={mdiFunctionVariant} />
           </svg>
         </Button>
       );
diff --git a/src/components/filter/FilterEditor.jsx b/src/components/filter/FilterEditor.jsx
index 01a0d8c..e11125b 100644
--- a/src/components/filter/FilterEditor.jsx
+++ b/src/components/filter/FilterEditor.jsx
@@ -11,6 +11,7 @@ import FilterEditorBlock from './FilterEditorBlock'
 import Button from '../Button'
 import SpecDoc from '../inputs/SpecDoc'
 import ExpressionProperty from '../fields/_ExpressionProperty';
+import {mdiFunctionVariant} from '@mdi/js';
 
 
 function combiningFilter (props) {
@@ -194,7 +195,7 @@ export default class CombiningFilterEditor extends React.Component {
           onClick={this.makeExpression}
         >
           <svg style={{marginRight: "0.2em", width:"14px", height:"14px", verticalAlign: "middle"}} viewBox="0 0 24 24">
-            <path fill="currentColor" d="M12.42,5.29C11.32,5.19 10.35,6 10.25,7.11L10,10H12.82V12H9.82L9.38,17.07C9.18,19.27 7.24,20.9 5.04,20.7C3.79,20.59 2.66,19.9 2,18.83L3.5,17.33C3.83,18.38 4.96,18.97 6,18.63C6.78,18.39 7.33,17.7 7.4,16.89L7.82,12H4.82V10H8L8.27,6.93C8.46,4.73 10.39,3.1 12.6,3.28C13.86,3.39 15,4.09 15.66,5.17L14.16,6.67C13.91,5.9 13.23,5.36 12.42,5.29M22,13.65L20.59,12.24L17.76,15.07L14.93,12.24L13.5,13.65L16.35,16.5L13.5,19.31L14.93,20.72L17.76,17.89L20.59,20.72L22,19.31L19.17,16.5L22,13.65Z" />
+            <path fill="currentColor" d={mdiFunctionVariant} />
           </svg>
           Upgrade to expression
         </Button>
@@ -212,7 +213,7 @@ export default class CombiningFilterEditor extends React.Component {
             className="maputnik-make-zoom-function"
           >
             <svg style={{width:"14px", height:"14px", verticalAlign: "middle"}} viewBox="0 0 24 24">
-              <path fill="currentColor" d="M12.42,5.29C11.32,5.19 10.35,6 10.25,7.11L10,10H12.82V12H9.82L9.38,17.07C9.18,19.27 7.24,20.9 5.04,20.7C3.79,20.59 2.66,19.9 2,18.83L3.5,17.33C3.83,18.38 4.96,18.97 6,18.63C6.78,18.39 7.33,17.7 7.4,16.89L7.82,12H4.82V10H8L8.27,6.93C8.46,4.73 10.39,3.1 12.6,3.28C13.86,3.39 15,4.09 15.66,5.17L14.16,6.67C13.91,5.9 13.23,5.36 12.42,5.29M22,13.65L20.59,12.24L17.76,15.07L14.93,12.24L13.5,13.65L16.35,16.5L13.5,19.31L14.93,20.72L17.76,17.89L20.59,20.72L22,19.31L19.17,16.5L22,13.65Z" />
+              <path fill="currentColor" d={mdiFunctionVariant} />
             </svg>
           </Button>
         </div>
diff --git a/src/styles/_components.scss b/src/styles/_components.scss
index 375f55f..eedefb5 100644
--- a/src/styles/_components.scss
+++ b/src/styles/_components.scss
@@ -252,3 +252,51 @@
     }
   }
 }
+
+.maputnik-inline-error {
+  color: #a4a4a4;
+  padding: 0.4em 0.4em;
+  font-size: 0.9em;
+  border: solid 1px $color-red;
+  border-radius: 2px;
+  margin: $margin-2 0px;
+}
+
+.maputnik-expression-editor {
+  border: solid 1px $color-gray;
+}
+
+.maputnik-input-block--wide {
+  .maputnik-input-block-content {
+    display: block;
+    width: auto;
+  }
+
+  .maputnik-input-block-label {
+    width: 82%;
+  }
+
+  .maputnik-input-block-action {
+    text-align: right;
+  }
+}
+
+.maputnik-expr-infobox {
+  font-size: $font-size-6;
+  background: $color-midgray;
+  padding: $margin-2;
+  border-radius: 2px;
+  border-top-right-radius: 0px;
+  border-top-left-radius: 0px;
+  color: $color-white;
+}
+
+.maputnik-expr-infobox__button {
+  background: none;
+  border: none;
+  padding: 0;
+  text-decoration: underline;
+  color: currentColor;
+  cursor: pointer;
+}
+
diff --git a/src/styles/index.scss b/src/styles/index.scss
index 2f027e1..11cca10 100644
--- a/src/styles/index.scss
+++ b/src/styles/index.scss
@@ -35,49 +35,3 @@
   height: 14px;
 }
 
-// TODO: Move these into correct *.scss files
-.maputnik-inline-error {
-  color: #a4a4a4;
-  padding: 0.4em 0.4em;
-  font-size: 0.9em;
-  border: solid 1px $color-red;
-  border-radius: 2px;
-  margin: $margin-2 0px;
-}
-
-.maputnik-expression-editor {
-  border: solid 1px $color-gray;
-}
-
-.maputnik-input-block--wide {
-  .maputnik-input-block-content {
-    display: block;
-    width: auto;
-  }
-
-  .maputnik-input-block-label {
-    width: 82%;
-  }
-
-  .maputnik-input-block-action {
-    text-align: right;
-  }
-}
-
-.maputnik-expr-infobox {
-  font-size: $font-size-6;
-  background: $color-midgray;
-  padding: $margin-2;
-  border-radius: 2px;
-  border-top-right-radius: 0px;
-  border-top-left-radius: 0px;
-  color: $color-white;
-}
-.maputnik-expr-infobox__button {
-  background: none;
-  border: none;
-  padding: 0;
-  text-decoration: underline;
-  color: currentColor;
-  cursor: pointer;
-}