diff --git a/chrome/content/zotero-platform/mac/overlay.css b/chrome/content/zotero-platform/mac/overlay.css
index e1cd1e9801..7d9898d854 100644
--- a/chrome/content/zotero-platform/mac/overlay.css
+++ b/chrome/content/zotero-platform/mac/overlay.css
@@ -190,13 +190,11 @@
 }
 
 #zotero-collections-tree treechildren::-moz-tree-twisty(selected) {
-	-moz-appearance: none;
-	list-style-image: url("chrome://zotero/skin/mac/twisty-selected.png");
+	list-style-image: url("chrome://zotero/skin/mac/twisty-selected.svg");
 }
 
 #zotero-collections-tree treechildren::-moz-tree-twisty(selected, open) {
-	-moz-appearance: none;
-	list-style-image: url("chrome://zotero/skin/mac/twisty-selected-open.png");
+	list-style-image: url("chrome://zotero/skin/mac/twisty-selected-open.svg");
 }
 
 #zotero-collections-splitter, #zotero-items-splitter
@@ -272,18 +270,18 @@
 
 treechildren::-moz-tree-twisty {
 	-moz-appearance: none;
-	width: 11px;
-	height: 11px;
-	list-style-image: url("chrome://zotero/skin/mac/twisty.png");
+	width: 16px;
+	height: 16px;
+	list-style-image: url("chrome://zotero/skin/mac/twisty.svg");
 	-moz-padding-start: 5px;
 	-moz-padding-end: 6px;
 }
 
 treechildren::-moz-tree-twisty(open) {
 	-moz-appearance: none;
-	width: 11px;
-	height: 11px;
-	list-style-image: url("chrome://zotero/skin/mac/twisty-open.png");
+	width: 16px;
+	height: 16px;
+	list-style-image: url("chrome://zotero/skin/mac/twisty-open.svg");
 	-moz-padding-start: 4px;
 	-moz-padding-end: 7px;
 }
@@ -291,23 +289,23 @@ treechildren::-moz-tree-twisty(open) {
 /* How to get active twisty?
 treechildren::-moz-tree-twisty(active) {
 	-moz-appearance: none;
-	list-style-image: url("chrome://zotero/skin/mac/twisty-active.png") !important;
+	list-style-image: url("chrome://zotero/skin/mac/twisty-active.svg") !important;
 }
 
 treechilren::-moz-tree-twisty(active) {
 	-moz-appearance: none;
-	list-style-image: url("chrome://zotero/skin/mac/twisty-active-open.png");
+	list-style-image: url("chrome://zotero/skin/mac/twisty-active-open.svg");
 }
 */
 
 tree:focus treechildren::-moz-tree-twisty(selected) {
 	-moz-appearance: none;
-	list-style-image: url("chrome://zotero/skin/mac/twisty-selected.png");
+	list-style-image: url("chrome://zotero/skin/mac/twisty-selected.svg");
 }
 
 tree:focus treechildren::-moz-tree-twisty(selected, open) {
 	-moz-appearance: none;
-	list-style-image: url("chrome://zotero/skin/mac/twisty-selected-open.png");
+	list-style-image: url("chrome://zotero/skin/mac/twisty-selected-open.svg");
 }
 
 treechildren::-moz-tree-image {
diff --git a/chrome/skin/default/zotero/mac/twisty-active-open.png b/chrome/skin/default/zotero/mac/twisty-active-open.png
deleted file mode 100644
index c5b13ed047..0000000000
Binary files a/chrome/skin/default/zotero/mac/twisty-active-open.png and /dev/null differ
diff --git a/chrome/skin/default/zotero/mac/twisty-active-open.svg b/chrome/skin/default/zotero/mac/twisty-active-open.svg
new file mode 100644
index 0000000000..2ac814534c
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty-active-open.svg
@@ -0,0 +1,15 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="#444">
+    <polyline points="3 4 12 4 7.5 12"/>
+    <g transform="translate(0,16)">
+      <polyline points="3 4 12 4 7.5 12" transform="rotate(-90, 7.5, 7.5)"/>
+    </g>
+  </g>
+</svg>
+
diff --git a/chrome/skin/default/zotero/mac/twisty-active.png b/chrome/skin/default/zotero/mac/twisty-active.png
deleted file mode 100644
index daaa60fe3a..0000000000
Binary files a/chrome/skin/default/zotero/mac/twisty-active.png and /dev/null differ
diff --git a/chrome/skin/default/zotero/mac/twisty-active.svg b/chrome/skin/default/zotero/mac/twisty-active.svg
new file mode 100644
index 0000000000..cb6d6f1318
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty-active.svg
@@ -0,0 +1,12 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="#444">
+    <polyline points="3 4 12 4 7.5 12" transform="rotate(-90, 7.5, 7.5)"/>
+  </g>
+</svg>
+
diff --git a/chrome/skin/default/zotero/mac/twisty-open.png b/chrome/skin/default/zotero/mac/twisty-open.png
deleted file mode 100644
index ec9b5ef05c..0000000000
Binary files a/chrome/skin/default/zotero/mac/twisty-open.png and /dev/null differ
diff --git a/chrome/skin/default/zotero/mac/twisty-open.svg b/chrome/skin/default/zotero/mac/twisty-open.svg
new file mode 100644
index 0000000000..0d3f7419d6
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty-open.svg
@@ -0,0 +1,11 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="#888">
+    <polyline points="3 4 12 4 7.5 12"/>
+  </g>
+</svg>
diff --git a/chrome/skin/default/zotero/mac/twisty-selected-active-open.svg b/chrome/skin/default/zotero/mac/twisty-selected-active-open.svg
new file mode 100644
index 0000000000..ebe88deb23
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty-selected-active-open.svg
@@ -0,0 +1,12 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="rgba(255, 255, 255, 0.7)">
+    <polyline points="3 4 12 4 7.5 12"/>
+  </g>
+</svg>
+
diff --git a/chrome/skin/default/zotero/mac/twisty-selected-active.svg b/chrome/skin/default/zotero/mac/twisty-selected-active.svg
new file mode 100644
index 0000000000..7a1c7992a8
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty-selected-active.svg
@@ -0,0 +1,12 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="rgba(255, 255, 255, 0.7)">
+    <polyline points="3 4 12 4 7.5 12" transform="rotate(-90, 7.5, 7.5)"/>
+  </g>
+</svg>
+
diff --git a/chrome/skin/default/zotero/mac/twisty-selected-open.png b/chrome/skin/default/zotero/mac/twisty-selected-open.png
deleted file mode 100644
index 484aa8f625..0000000000
Binary files a/chrome/skin/default/zotero/mac/twisty-selected-open.png and /dev/null differ
diff --git a/chrome/skin/default/zotero/mac/twisty-selected-open.svg b/chrome/skin/default/zotero/mac/twisty-selected-open.svg
new file mode 100644
index 0000000000..827272d266
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty-selected-open.svg
@@ -0,0 +1,12 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="#FFF">
+    <polyline points="3 4 12 4 7.5 12"/>
+  </g>
+</svg>
+
diff --git a/chrome/skin/default/zotero/mac/twisty-selected.png b/chrome/skin/default/zotero/mac/twisty-selected.png
deleted file mode 100644
index b7d58a4ee1..0000000000
Binary files a/chrome/skin/default/zotero/mac/twisty-selected.png and /dev/null differ
diff --git a/chrome/skin/default/zotero/mac/twisty-selected.svg b/chrome/skin/default/zotero/mac/twisty-selected.svg
new file mode 100644
index 0000000000..a14e9b8040
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty-selected.svg
@@ -0,0 +1,12 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="#FFF">
+    <polyline points="3 4 12 4 7.5 12" transform="rotate(-90, 7.5, 7.5)"/>
+  </g>
+</svg>
+
diff --git a/chrome/skin/default/zotero/mac/twisty.png b/chrome/skin/default/zotero/mac/twisty.png
deleted file mode 100644
index c4af03f310..0000000000
Binary files a/chrome/skin/default/zotero/mac/twisty.png and /dev/null differ
diff --git a/chrome/skin/default/zotero/mac/twisty.svg b/chrome/skin/default/zotero/mac/twisty.svg
new file mode 100644
index 0000000000..d54abaff4e
--- /dev/null
+++ b/chrome/skin/default/zotero/mac/twisty.svg
@@ -0,0 +1,12 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+	 - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<svg  xmlns="http://www.w3.org/2000/svg"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      width="16" height="16" viewBox="0 0 16 16">
+  <g fill="#888">
+    <polyline points="3 4 12 4 7.5 12" transform="rotate(-90, 7.5, 7.5)"/>
+  </g>
+</svg>
+