Restyle UI with modern glassy theme

frontend/src/css/buttons.css

@@ -1,24 +1,31 @@
 button {
-  padding: 10px 20px;
-  border: none;
-  border-radius: 5px;
-  margin: 5px;
+  padding: 12px 18px;
+  border-radius: 14px;
+  border: 1px solid transparent;
+  margin: 6px 4px;
   cursor: pointer;
-  font-weight: bold;
-}
-
-body:not(.dark-mode) button {
-  background-color: #f0f0f0;
-  color: #333;
-  border: 1px solid #ccc;
-}
-
-body.dark-mode button {
-  background-color: #444;
-  color: #fff;
-  border: 1px solid #888;
+  font-weight: 600;
+  font-size: 1rem;
+  letter-spacing: 0.01em;
+  background: linear-gradient(135deg, var(--accent) 0%, var(--accent-strong) 100%);
+  color: #0b1224;
+  box-shadow: 0 12px 30px rgba(14, 165, 233, 0.32);
+  transition: transform 0.15s ease, box-shadow 0.2s ease, filter 0.2s ease;
 }
 
 button:hover {
-  background-color: #ccc;
-}
+  transform: translateY(-1px);
+  box-shadow: 0 16px 32px rgba(14, 165, 233, 0.38);
+  filter: brightness(1.03);
+}
+
+button:active {
+  transform: translateY(0);
+  box-shadow: 0 10px 20px rgba(14, 165, 233, 0.28);
+}
+
+button:disabled {
+  opacity: 0.55;
+  cursor: not-allowed;
+  box-shadow: none;
+}