(style): Refactor HTML templates and add CSS

Refactored HTML templates for improved strucutre and clarity
Moved styles to a separate CSS file for better maintainablilty

static/css/style.css

@@ -0,0 +1,55 @@
+body {
+    font-family: Arial, sans-serif;
+    padding: 20px;
+  }
+  
+  table {
+    border-collapse: collapse;
+    width: 100%;
+  }
+  
+  th,
+  td {
+    border: 1px solid #ddd;
+    padding: 8px;
+    text-align: left;
+  }
+  
+  th {
+    background-color: #f2f2f2;
+  }
+  
+  a {
+    margin-right: 10px;
+  }
+  
+  form {
+    max-width: 600px;
+    margin: 0 auto;
+  }
+  
+  label {
+    display: block;
+    margin-top: 15px;
+  }
+  
+  input[type="text"],
+  input[type="password"],
+  textarea {
+    width: 100%;
+    padding: 8px;
+  }
+  
+  button {
+    margin-top: 15px;
+    padding: 10px 20px;
+  }
+  
+  .flash {
+    background-color: #f8d7da;
+    color: #721c24;
+    padding: 10px;
+    margin-bottom: 10px;
+    text-align: center;
+  }
+