diff --git a/web-crypto/derive-bits/ecdh.js b/web-crypto/derive-bits/ecdh.js
index 0b565be..217250c 100644
--- a/web-crypto/derive-bits/ecdh.js
+++ b/web-crypto/derive-bits/ecdh.js
@@ -16,7 +16,7 @@
     sharedSecretValue.classList.add("fade-in");
     sharedSecretValue.addEventListener("animationend", () => {
       sharedSecretValue.classList.remove("fade-in");
-    });
+    }, { once: true });
     sharedSecretValue.textContent = `${buffer}...[${sharedSecret.byteLength} bytes total]`;
   }
 
diff --git a/web-crypto/derive-bits/pbkdf2.js b/web-crypto/derive-bits/pbkdf2.js
index 80037e9..748200b 100644
--- a/web-crypto/derive-bits/pbkdf2.js
+++ b/web-crypto/derive-bits/pbkdf2.js
@@ -40,7 +40,7 @@
     derivedBitsValue.classList.add("fade-in");
     derivedBitsValue.addEventListener("animationend", () => {
       derivedBitsValue.classList.remove("fade-in");
-    });
+    }, { once: true });
     derivedBitsValue.textContent = `${buffer}...[${derivedBits.byteLength} bytes total]`;
   }
 
diff --git a/web-crypto/derive-key/ecdh.js b/web-crypto/derive-key/ecdh.js
index 3a4fd81..83cb705 100644
--- a/web-crypto/derive-key/ecdh.js
+++ b/web-crypto/derive-key/ecdh.js
@@ -39,7 +39,7 @@
     ciphertextValue.classList.add("fade-in");
     ciphertextValue.addEventListener("animationend", () => {
       ciphertextValue.classList.remove("fade-in");
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -69,7 +69,7 @@
       decryptedValue.classList.add("fade-in");
       decryptedValue.addEventListener("animationend", () => {
         decryptedValue.classList.remove("fade-in");
-      });
+      }, { once: true });
       decryptedValue.textContent = dec.decode(decrypted);
     } catch (e) {
       decryptedValue.classList.add("error");
diff --git a/web-crypto/derive-key/pbkdf2.js b/web-crypto/derive-key/pbkdf2.js
index ba167c9..8d1f65c 100644
--- a/web-crypto/derive-key/pbkdf2.js
+++ b/web-crypto/derive-key/pbkdf2.js
@@ -80,7 +80,7 @@
     ciphertextValue.classList.add("fade-in");
     ciphertextValue.addEventListener("animationend", () => {
       ciphertextValue.classList.remove("fade-in");
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -114,7 +114,7 @@
       decryptedValue.classList.add("fade-in");
       decryptedValue.addEventListener("animationend", () => {
         decryptedValue.classList.remove("fade-in");
-      });
+      }, { once: true });
       decryptedValue.textContent = dec.decode(decrypted);
     } catch (e) {
       decryptedValue.classList.add("error");
diff --git a/web-crypto/encrypt-decrypt/aes-cbc.js b/web-crypto/encrypt-decrypt/aes-cbc.js
index 0fcfe78..f760490 100644
--- a/web-crypto/encrypt-decrypt/aes-cbc.js
+++ b/web-crypto/encrypt-decrypt/aes-cbc.js
@@ -39,7 +39,7 @@
     ciphertextValue.classList.add('fade-in');
     ciphertextValue.addEventListener('animationend', () => {
       ciphertextValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -62,7 +62,7 @@
     decryptedValue.classList.add('fade-in');
     decryptedValue.addEventListener('animationend', () => {
       decryptedValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     decryptedValue.textContent = dec.decode(decrypted);
   }
 
diff --git a/web-crypto/encrypt-decrypt/aes-ctr.js b/web-crypto/encrypt-decrypt/aes-ctr.js
index 8079dd2..0a522fd 100644
--- a/web-crypto/encrypt-decrypt/aes-ctr.js
+++ b/web-crypto/encrypt-decrypt/aes-ctr.js
@@ -40,7 +40,7 @@
     ciphertextValue.classList.add('fade-in');
     ciphertextValue.addEventListener('animationend', () => {
       ciphertextValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -64,7 +64,7 @@
     decryptedValue.classList.add('fade-in');
     decryptedValue.addEventListener('animationend', () => {
       decryptedValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     decryptedValue.textContent = dec.decode(decrypted);
   }
 
diff --git a/web-crypto/encrypt-decrypt/aes-gcm.js b/web-crypto/encrypt-decrypt/aes-gcm.js
index 4ac03ee..bbaf969 100644
--- a/web-crypto/encrypt-decrypt/aes-gcm.js
+++ b/web-crypto/encrypt-decrypt/aes-gcm.js
@@ -39,7 +39,7 @@
     ciphertextValue.classList.add('fade-in');
     ciphertextValue.addEventListener('animationend', () => {
       ciphertextValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -62,7 +62,7 @@
     decryptedValue.classList.add('fade-in');
     decryptedValue.addEventListener('animationend', () => {
       decryptedValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     decryptedValue.textContent = dec.decode(decrypted);
   }
 
diff --git a/web-crypto/encrypt-decrypt/rsa-oaep.js b/web-crypto/encrypt-decrypt/rsa-oaep.js
index fd9823b..d676154 100644
--- a/web-crypto/encrypt-decrypt/rsa-oaep.js
+++ b/web-crypto/encrypt-decrypt/rsa-oaep.js
@@ -35,7 +35,7 @@
     ciphertextValue.classList.add('fade-in');
     ciphertextValue.addEventListener('animationend', () => {
       ciphertextValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -57,7 +57,7 @@
     decryptedValue.classList.add('fade-in');
     decryptedValue.addEventListener('animationend', () => {
       decryptedValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     decryptedValue.textContent = dec.decode(decrypted);
   }
 
diff --git a/web-crypto/export-key/jwk.js b/web-crypto/export-key/jwk.js
index a7cbf6e..7d9b429 100644
--- a/web-crypto/export-key/jwk.js
+++ b/web-crypto/export-key/jwk.js
@@ -12,7 +12,7 @@
     exportKeyOutput.classList.add("fade-in");
     exportKeyOutput.addEventListener("animationend", () => {
       exportKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     exportKeyOutput.textContent = JSON.stringify(exported, null, " ");
   }
 
diff --git a/web-crypto/export-key/pkcs8.js b/web-crypto/export-key/pkcs8.js
index b71174e..e2505b2 100644
--- a/web-crypto/export-key/pkcs8.js
+++ b/web-crypto/export-key/pkcs8.js
@@ -24,7 +24,7 @@
     exportKeyOutput.classList.add("fade-in");
     exportKeyOutput.addEventListener("animationend", () => {
       exportKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     exportKeyOutput.textContent = pemExported;
   }
 
diff --git a/web-crypto/export-key/raw.js b/web-crypto/export-key/raw.js
index 5892020..52f134a 100644
--- a/web-crypto/export-key/raw.js
+++ b/web-crypto/export-key/raw.js
@@ -14,7 +14,7 @@
     exportKeyOutput.classList.add("fade-in");
     exportKeyOutput.addEventListener("animationend", () => {
       exportKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     exportKeyOutput.textContent = `[${exportedKeyBuffer}]`;
   }
 
diff --git a/web-crypto/export-key/spki.js b/web-crypto/export-key/spki.js
index d785f0e..b429e67 100644
--- a/web-crypto/export-key/spki.js
+++ b/web-crypto/export-key/spki.js
@@ -24,7 +24,7 @@
     exportKeyOutput.classList.add("fade-in");
     exportKeyOutput.addEventListener("animationend", () => {
       exportKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     exportKeyOutput.textContent = pemExported;
   }
 
diff --git a/web-crypto/import-key/jwk.js b/web-crypto/import-key/jwk.js
index 75608b7..90c2d08 100644
--- a/web-crypto/import-key/jwk.js
+++ b/web-crypto/import-key/jwk.js
@@ -65,7 +65,7 @@
       signatureValue.classList.add('fade-in');
       signatureValue.addEventListener('animationend', () => {
         signatureValue.classList.remove('fade-in');
-      });
+      }, { once: true });
       const buffer = new Uint8Array(signature, 0, 5);
       signatureValue.textContent = `${buffer}...[${signature.byteLength} bytes total]`;
     }
@@ -77,7 +77,7 @@
       signButton.classList.add('fade-in');
       signButton.addEventListener('animationend', () => {
         signButton.classList.remove('fade-in');
-      });
+      }, { once: true });
       signButton.removeAttribute("disabled");
       signButton.classList.remove("hidden");
     }
diff --git a/web-crypto/import-key/pkcs8.js b/web-crypto/import-key/pkcs8.js
index 57fc466..42d210e 100644
--- a/web-crypto/import-key/pkcs8.js
+++ b/web-crypto/import-key/pkcs8.js
@@ -84,7 +84,7 @@ MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDD0tPV/du2vftjvXj1t/gXTK39sNBV
     signatureValue.classList.add('fade-in');
     signatureValue.addEventListener('animationend', () => {
       signatureValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     const buffer = new Uint8Array(signature, 0, 5);
     signatureValue.textContent = `${buffer}...[${signature.byteLength} bytes total]`;
   }
@@ -96,7 +96,7 @@ MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDD0tPV/du2vftjvXj1t/gXTK39sNBV
     signButton.classList.add('fade-in');
     signButton.addEventListener('animationend', () => {
       signButton.classList.remove('fade-in');
-    });
+    }, { once: true });
     signButton.removeAttribute("disabled");
     signButton.classList.remove("hidden");
   }
diff --git a/web-crypto/import-key/raw.js b/web-crypto/import-key/raw.js
index 275646b..4a1b875 100644
--- a/web-crypto/import-key/raw.js
+++ b/web-crypto/import-key/raw.js
@@ -57,7 +57,7 @@
     ciphertextValue.classList.add('fade-in');
     ciphertextValue.addEventListener('animationend', () => {
       ciphertextValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -68,7 +68,7 @@
       encryptButton.classList.add('fade-in');
       encryptButton.addEventListener('animationend', () => {
         encryptButton.classList.remove('fade-in');
-      });
+      }, { once: true });
       encryptButton.removeAttribute("disabled");
       encryptButton.classList.remove("hidden");
     }
diff --git a/web-crypto/import-key/spki.js b/web-crypto/import-key/spki.js
index cfe8353..b6ccf53 100644
--- a/web-crypto/import-key/spki.js
+++ b/web-crypto/import-key/spki.js
@@ -81,7 +81,7 @@ MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAy3Xo3U13dc+xojwQYWoJLCbOQ5fOVY8Llnqc
     ciphertextValue.classList.add('fade-in');
     ciphertextValue.addEventListener('animationend', () => {
       ciphertextValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -92,7 +92,7 @@ MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAy3Xo3U13dc+xojwQYWoJLCbOQ5fOVY8Llnqc
     encryptButton.classList.add('fade-in');
     encryptButton.addEventListener('animationend', () => {
       encryptButton.classList.remove('fade-in');
-    });
+    }, { once: true });
     encryptButton.removeAttribute("disabled");
     encryptButton.classList.remove("hidden");
   }
diff --git a/web-crypto/sign-verify/ecdsa.js b/web-crypto/sign-verify/ecdsa.js
index abb87ce..5ab867f 100644
--- a/web-crypto/sign-verify/ecdsa.js
+++ b/web-crypto/sign-verify/ecdsa.js
@@ -37,7 +37,7 @@
     signatureValue.classList.add('fade-in');
     signatureValue.addEventListener('animationend', () => {
       signatureValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     let buffer = new Uint8Array(signature, 0, 5);
     signatureValue.textContent = `${buffer}...[${signature.byteLength} bytes total]`;
   }
diff --git a/web-crypto/sign-verify/hmac.js b/web-crypto/sign-verify/hmac.js
index 5d6d894..5481d5b 100644
--- a/web-crypto/sign-verify/hmac.js
+++ b/web-crypto/sign-verify/hmac.js
@@ -34,7 +34,7 @@
     signatureValue.classList.add('fade-in');
     signatureValue.addEventListener('animationend', () => {
       signatureValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     let buffer = new Uint8Array(signature, 0, 5);
     signatureValue.textContent = `${buffer}...[${signature.byteLength} bytes total]`;
   }
diff --git a/web-crypto/sign-verify/rsa-pss.js b/web-crypto/sign-verify/rsa-pss.js
index b485921..c2a33e4 100644
--- a/web-crypto/sign-verify/rsa-pss.js
+++ b/web-crypto/sign-verify/rsa-pss.js
@@ -37,7 +37,7 @@
     signatureValue.classList.add('fade-in');
     signatureValue.addEventListener('animationend', () => {
       signatureValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     let buffer = new Uint8Array(signature, 0, 5);
     signatureValue.textContent = `${buffer}...[${signature.byteLength} bytes total]`;
   }
diff --git a/web-crypto/sign-verify/rsassa-pkcs1.js b/web-crypto/sign-verify/rsassa-pkcs1.js
index e215ba6..0127ada 100644
--- a/web-crypto/sign-verify/rsassa-pkcs1.js
+++ b/web-crypto/sign-verify/rsassa-pkcs1.js
@@ -34,7 +34,7 @@
     signatureValue.classList.add('fade-in');
     signatureValue.addEventListener('animationend', () => {
       signatureValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     let buffer = new Uint8Array(signature, 0, 5);
     signatureValue.textContent = `${buffer}...[${signature.byteLength} bytes total]`;
   }
diff --git a/web-crypto/unwrap-key/pkcs8.js b/web-crypto/unwrap-key/pkcs8.js
index d3bbed6..2b41719 100644
--- a/web-crypto/unwrap-key/pkcs8.js
+++ b/web-crypto/unwrap-key/pkcs8.js
@@ -198,7 +198,7 @@
     signatureValue.classList.add('fade-in');
     signatureValue.addEventListener('animationend', () => {
       signatureValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     const buffer = new Uint8Array(signature, 0, 5);
     signatureValue.textContent = `${buffer}...[${signature.byteLength} bytes total]`;
   }
@@ -218,7 +218,7 @@
     signButton.classList.add('fade-in');
     signButton.addEventListener('animationend', () => {
       signButton.classList.remove('fade-in');
-    });
+    }, { once: true });
     signButton.removeAttribute("disabled");
     signButton.classList.remove("hidden");
   }
diff --git a/web-crypto/unwrap-key/raw.js b/web-crypto/unwrap-key/raw.js
index de7f9bf..8b78534 100644
--- a/web-crypto/unwrap-key/raw.js
+++ b/web-crypto/unwrap-key/raw.js
@@ -128,7 +128,7 @@
     ciphertextValue.classList.add('fade-in');
     ciphertextValue.addEventListener('animationend', () => {
       ciphertextValue.classList.remove('fade-in');
-    });
+    }, { once: true });
     ciphertextValue.textContent = `${buffer}...[${ciphertext.byteLength} bytes total]`;
   }
 
@@ -147,7 +147,7 @@
     encryptButton.classList.add('fade-in');
     encryptButton.addEventListener('animationend', () => {
       encryptButton.classList.remove('fade-in');
-    });
+    }, { once: true });
     encryptButton.removeAttribute("disabled");
     encryptButton.classList.remove("hidden");
   }
diff --git a/web-crypto/wrap-key/jwk.js b/web-crypto/wrap-key/jwk.js
index 66d4307..d1027fc 100644
--- a/web-crypto/wrap-key/jwk.js
+++ b/web-crypto/wrap-key/jwk.js
@@ -64,7 +64,7 @@
     wrappedKeyOutput.classList.add("fade-in");
     wrappedKeyOutput.addEventListener("animationend", () => {
       wrappedKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     wrappedKeyOutput.textContent = `[${wrappedKeyBuffer}]`;
   }
 
diff --git a/web-crypto/wrap-key/pkcs8.js b/web-crypto/wrap-key/pkcs8.js
index 7ca5ba8..3bab44b 100644
--- a/web-crypto/wrap-key/pkcs8.js
+++ b/web-crypto/wrap-key/pkcs8.js
@@ -64,7 +64,7 @@
     wrappedKeyOutput.classList.add("fade-in");
     wrappedKeyOutput.addEventListener("animationend", () => {
       wrappedKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     wrappedKeyOutput.textContent = `[${wrappedKeyBuffer}]`;
   }
 
diff --git a/web-crypto/wrap-key/raw.js b/web-crypto/wrap-key/raw.js
index a6ff74c..b8c493e 100644
--- a/web-crypto/wrap-key/raw.js
+++ b/web-crypto/wrap-key/raw.js
@@ -59,7 +59,7 @@
     wrappedKeyOutput.classList.add("fade-in");
     wrappedKeyOutput.addEventListener("animationend", () => {
       wrappedKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     wrappedKeyOutput.textContent = `[${wrappedKeyBuffer}]`;
   }
 
diff --git a/web-crypto/wrap-key/spki.js b/web-crypto/wrap-key/spki.js
index 1cd874c..3b9cd3b 100644
--- a/web-crypto/wrap-key/spki.js
+++ b/web-crypto/wrap-key/spki.js
@@ -64,7 +64,7 @@
     wrappedKeyOutput.classList.add("fade-in");
     wrappedKeyOutput.addEventListener("animationend", () => {
       wrappedKeyOutput.classList.remove("fade-in");
-    });
+    }, { once: true });
     wrappedKeyOutput.textContent = `[${wrappedKeyBuffer}]`;
   }