copied math toggle button from commit 721d9883 and improved code + clarity (see #243)

frontend/src/components/submission_notes/toolbars/AnnotatedSubmissionTopToolbar.vue

@@ -23,9 +23,22 @@
       Score: {{ score }} </span>
     <v-spacer />
     <toggle-feedback-visibility-button />
+    <v-spacer />
     <div v-if="isMarkdown">
-      <v-btn @click="$emit('input', !mathIsRendered)">
-        {{ mathIsRendered ? 'Reset Math' : 'Render Math' }}
+			<v-btn
+				text
+        title="Toggle Math Renderer"
+        :style="{
+					// 'info' color doesn't work here for some reason
+					color: mathIsRendered ? '#4281F5' : 'gray',
+					backgroundColor: mathIsRendered ? '#CCE7FF' : '#E0E0E0'
+				}"
+        @click="$emit('input', !mathIsRendered)"
+      >
+        <v-icon>
+          functions
+          {{ mathIsRendered ? "check_circle_outline" : "highlight_off"}}
+        </v-icon>
       </v-btn>
     </div>
     <v-spacer />