Fix style of selector

apps/client/src/app/pages/portfolio/fire/fire-page.scss

@@ -1,12 +1,17 @@
 @use '../../../../styles/variables.scss' as variables;
 
+@mixin select-arrow($color) {
+  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='10' height='6' fill='#{$color}'><polygon points='0,0 10,0 5,6'/></svg>");
+}
+
 :host {
   display: block;
 
   .safe-withdrawal-rate-select {
+    @include select-arrow(variables.$dark-primary-text);
+
     appearance: none;
     background-color: transparent;
-    background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='10' height='6' fill='#{variables.$dark-primary-text}'><polygon points='0,0 10,0 5,6'/></svg>");
     background-position: right 0 center;
     background-repeat: no-repeat;
     color: rgb(var(--dark-primary-text));
@@ -21,7 +26,8 @@
 
 :host-context(.theme-dark) {
   .safe-withdrawal-rate-select {
-    background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='10' height='6' fill='#{variables.$light-primary-text}'><polygon points='0,0 10,0 5,6'/></svg>");
+    @include select-arrow(variables.$light-primary-text);
+
     color: rgb(var(--light-primary-text));
   }
 }