Creation of side-menu.

frontend/src/app/components/side-menu/side-menu.component.scss

@@ -0,0 +1,52 @@
+:host {
+    display: flex;
+    flex-direction: column;
+
+    .categories-container {
+        display: flex;
+        flex-direction: column;
+
+        .category {
+            border: 1px solid blue;
+
+            &:hover {
+                cursor: pointer;
+            }
+
+            .category-header {
+                display: flex;
+                flex-direction: row;
+                justify-content: space-between;
+                align-items: center;
+                padding: .5em 1em;
+
+                mat-icon {
+                    transition: transform .2s ease-in-out;
+                }
+            }
+
+            &.openned {
+                .category-header {
+                    mat-icon {
+                        transform: rotate(90deg);
+                    }
+                }
+
+                .sub-category-container {
+                    max-height: none;
+                }
+            }
+
+            .sub-category-container {
+                border: 1px solid red;
+                overflow: hidden;
+                max-height: 0;
+                transition: max-height .2s ease-in-out;
+    
+                .sub-category {
+                    padding: .5em 1em .5em 2em;
+                }
+            }
+        }
+    }
+}