feat: use input element directly

Previously, a button proxy was used which required the use of complicated reference management. Using the HTML `input` element directly simplifies the implementation.

Also moved some styles.

ref: N25B-189

src/pages/VisProgPage/visualProgrammingUI/components/SaveLoadPanel.module.css

@@ -0,0 +1,30 @@
+.save-load-panel {
+  border-radius: 0 0 5pt 5pt;
+  background-color: canvas;
+}
+
+label.file-input-button {
+  cursor: pointer;
+  outline: forestgreen solid 2pt;
+  filter: drop-shadow(0 0 0.25rem forestgreen);
+  transition: filter 200ms;
+
+  input[type="file"] {
+    display: none;
+  }
+
+  &:hover {
+    filter: drop-shadow(0 0 0.5rem forestgreen);
+  }
+}
+
+.save-button {
+  text-decoration: none;
+  outline: dodgerblue solid 2pt;
+  filter: drop-shadow(0 0 0.25rem dodgerblue);
+  transition: filter 200ms;
+
+  &:hover {
+    filter: drop-shadow(0 0 0.5rem dodgerblue);
+  }
+}