style: add button style

 .header {
-  height: 70px;
+  width: 100%;
+  height: 90px;
   display: flex;
+  flex-direction: column;
   justify-content: center;
   align-items: center;
   font-size: 1.8rem;
-  width: 100%;
-}
\ No newline at end of file
+
+  .form-container {
+    width: 200px;
+    height: 100%;
+    display: flex;
+    flex-direction: column;
+    justify-content: center;
+    align-items: center;
+
+    #id-input {
+      height: 100%;
+      text-align: center;
+      font-size: 21px;
+      border: none;
+
+      &:focus {
+        outline: none;
+      }
+    }
+
+    button {
+      width: 100%;
+      margin: 8px 0;
+      padding: 6px;
+      background-color: deepskyblue;
+      color: #efefef;
+      border: none;
+      border-radius: 6px;
+    }
+  }
+}

@@ -33,16 +33,16 @@
 
     .followers {
       flex: 1;
-      padding: .4rem;
+      padding: 0.4rem;
     }
     .following {
       flex: 1;
-      padding: .4rem;
+      padding: 0.4rem;
     }
 
     .item {
       padding-left: 0.3rem;
-      margin: .25rem 0;
+      margin: 0.25rem 0;
       border-radius: 0.16rem;
       height: 1.8rem;
       display: flex;
@@ -60,4 +60,4 @@
     font-weight: 800;
     margin: 0.5rem 0;
   }
-}
\ No newline at end of file
+}