feat: add new frontend skeleton

+body {
+  font-size: .875rem;
+}
+
+.login-html, .login-body {
+  height: 100%;
+}
+
+.login-body {
+  display: -ms-flexbox;
+  display: flex;
+  -ms-flex-align: center;
+  align-items: center;
+  padding-top: 40px;
+  padding-bottom: 40px;
+  background-color: #f5f5f5;
+}
+
+.form-signin {
+  width: 100%;
+  max-width: 330px;
+  padding: 15px;
+  margin: auto;
+}
+.form-signin .checkbox {
+  font-weight: 400;
+}
+.form-signin .form-control {
+  position: relative;
+  box-sizing: border-box;
+  height: auto;
+  padding: 10px;
+  font-size: 16px;
+}
+.form-signin .form-control:focus {
+  z-index: 2;
+}
+.form-signin .input-top {
+  margin-bottom: -1px;
+  border-bottom-right-radius: 0;
+  border-bottom-left-radius: 0;
+}
+.form-signin .input-mid {
+  margin-bottom: -1px;
+  border-radius: 0;
+}
+.form-signin .input-bot {
+  margin-bottom: 10px;
+  border-top-left-radius: 0;
+  border-top-right-radius: 0;
+}
+
+.feather {
+  width: 16px;
+  height: 16px;
+  vertical-align: text-bottom;
+}
+
+/*
+ * Sidebar
+ */
+
+.sidebar {
+  position: fixed;
+  top: 0;
+  bottom: 0;
+  left: 0;
+  z-index: 100; /* Behind the navbar */
+  padding: 48px 0 0; /* Height of navbar */
+  box-shadow: inset -1px 0 0 rgba(0, 0, 0, .1);
+}
+
+@media (max-width: 767.98px) {
+  .sidebar {
+    top: 5rem;
+  }
+}
+
+.sidebar-sticky {
+  position: relative;
+  top: 0;
+  height: calc(100vh - 48px);
+  padding-top: .5rem;
+  overflow-x: hidden;
+  overflow-y: auto; /* Scrollable contents if viewport is shorter than content. */
+}
+
+@supports ((position: -webkit-sticky) or (position: sticky)) {
+  .sidebar-sticky {
+    position: -webkit-sticky;
+    position: sticky;
+  }
+}
+
+.sidebar .nav-link {
+  font-weight: 500;
+  color: #333;
+}
+
+.sidebar .nav-link .feather {
+  margin-right: 4px;
+  color: #999;
+}
+
+.sidebar .nav-link.active {
+  color: #007bff;
+}
+
+.sidebar .nav-link:hover .feather,
+.sidebar .nav-link.active .feather {
+  color: inherit;
+}
+
+.sidebar-heading {
+  font-size: .75rem;
+  text-transform: uppercase;
+}
+
+/*
+ * Navbar
+ */
+
+.navbar-brand {
+  padding-top: .75rem;
+  padding-bottom: .75rem;
+  font-size: 1rem;
+  background-color: rgba(0, 0, 0, .25);
+  box-shadow: inset -1px 0 0 rgba(0, 0, 0, .25);
+}
+
+.navbar .navbar-toggler {
+  top: .25rem;
+  right: 1rem;
+}
+
+.navbar .form-control {
+  padding: .75rem 1rem;
+  border-width: 0;
+  border-radius: 0;
+}
+
+.form-control-dark {
+  color: #fff;
+  background-color: rgba(255, 255, 255, .1);
+  border-color: rgba(255, 255, 255, .1);
+}
+
+.form-control-dark:focus {
+  border-color: transparent;
+  box-shadow: 0 0 0 3px rgba(255, 255, 255, .25);
+}
+
+.dropdown-item {
+  font-size: 0.8rem;
+}