FIX: add missing hamburger button to HTML

Author: hyeondo-jang

contact.html

@@ -121,9 +121,6 @@
             margin-bottom: 4px;
         }
 
-        nav.collapsed {
-            display: none;
-        }
 
         @media (max-width: 640px) {
             .inner {
@@ -182,6 +179,7 @@
 
     <header>
         <a href="index.html" class="lab-name">Lee Optimization Group</a>
+        <button class="menu-toggle" aria-label="Menu">&#9776;</button>
         <nav>
             <a href="index.html">Home</a>
             <a href="research.html">Research</a>

group.html

@@ -218,9 +218,6 @@
             margin-bottom: 4px;
         }
 
-        nav.collapsed {
-            display: none;
-        }
 
         @media (max-width: 640px) {
             .inner {
@@ -279,6 +276,7 @@
 
     <header>
         <a href="index.html" class="lab-name">Lee Optimization Group</a>
+        <button class="menu-toggle" aria-label="Menu">&#9776;</button>
         <nav>
             <a href="index.html">Home</a>
             <a href="research.html">Research</a>

hiring.html

@@ -159,9 +159,6 @@
             margin-bottom: 4px;
         }
 
-        nav.collapsed {
-            display: none;
-        }
 
         @media (max-width: 640px) {
             .inner {
@@ -220,6 +217,7 @@
 
     <header>
         <a href="index.html" class="lab-name">Lee Optimization Group</a>
+        <button class="menu-toggle" aria-label="Menu">&#9776;</button>
         <nav>
             <a href="index.html">Home</a>
             <a href="research.html">Research</a>

index.html

@@ -195,9 +195,6 @@
             margin-bottom: 4px;
         }
 
-        nav.collapsed {
-            display: none;
-        }
 
         @media (max-width: 640px) {
             .inner {
@@ -256,6 +253,7 @@
 
     <header>
         <span class="lab-name">Lee Optimization Group</span>
+        <button class="menu-toggle" aria-label="Menu">&#9776;</button>
         <nav>
             <a href="index.html">Home</a>
             <a href="research.html">Research</a>

publications.html

@@ -163,9 +163,6 @@
             margin-bottom: 4px;
         }
 
-        nav.collapsed {
-            display: none;
-        }
 
         @media (max-width: 640px) {
             .inner {
@@ -224,6 +221,7 @@
 
     <header>
         <a href="index.html" class="lab-name">Lee Optimization Group</a>
+        <button class="menu-toggle" aria-label="Menu">&#9776;</button>
         <nav>
             <a href="index.html">Home</a>
             <a href="research.html">Research</a>

research.html

@@ -165,9 +165,6 @@
             margin-bottom: 4px;
         }
 
-        nav.collapsed {
-            display: none;
-        }
 
         @media (max-width: 640px) {
             .inner {
@@ -226,6 +223,7 @@
 
     <header>
         <a href="index.html" class="lab-name">Lee Optimization Group</a>
+        <button class="menu-toggle" aria-label="Menu">&#9776;</button>
         <nav>
             <a href="index.html">Home</a>
             <a href="research.html">Research</a>