Set a z-index for the fullscreen modals to avoid glitches with the sticky menu

Otherwise the sticky menu is on top of the modal.

src/dbp-official-signature-pdf-upload.js

@@ -563,6 +563,7 @@ class OfficialSignaturePdfUpload extends ScopedElementsMixin(DBPSignatureLitElem
                 /* Modal preview, upload and external auth */
                 div.right-container > * {
                     position: fixed;
+                    z-index: 1000;
                     padding: 10px;
                     top: 0;
                     left: 0;

src/dbp-qualified-signature-pdf-upload.js

@@ -704,6 +704,7 @@ class QualifiedSignaturePdfUpload extends ScopedElementsMixin(DBPSignatureLitEle
                 /* Modal preview, upload and external auth */
                 div.right-container > * {
                     position: fixed;
+                    z-index: 1000;
                     padding: 10px;
                     top: 0;
                     left: 0;

src/dbp-signature-verification-full.js

@@ -515,6 +515,7 @@ class SignatureVerificationFull extends ScopedElementsMixin(DBPSignatureLitEleme
                 /* Modal preview, upload and external auth */
                 div.right-container > * {
                     position: fixed;
+                    z-index: 1000;
                     padding: 10px;
                     top: 0;
                     left: 0;