[feature] decouple login.scss from variables (#93)

Preparing for a switch to CSS variables

- decouple login.scss from variables.scss
- move scrollbar css to separate file

Reviewed-on: https://codeberg.org/superseriousbusiness/masto-fe-standalone/pulls/93
Co-authored-by: Zoë Bijl <code@moiety.me>
Co-committed-by: Zoë Bijl <code@moiety.me>

app/javascript/flavours/glitch/styles/login.scss

@@ -1,13 +1,17 @@
-@import 'variables';
 @import 'styles/fonts/roboto';
-@import 'styles/fonts/roboto-mono';
 @import 'reset';
-@import 'basics';
+
+:root {
+    --color-bg: #191b22;
+    --color-fg: #fff;
+}
 
 body {
+    color: var(--color-fg);
     font-family: ui-rounded, mastodon-font-sans-serif, sans-serif;
     font-size: 1rem;
     line-height: 1.5;
+    background: var(--color-bg);
 }
 
 .login-container {
@@ -45,7 +49,7 @@ h1 {
 
 label {
     font-family: inherit;
-    color: $primary-text-color;
+    color: var(--color-fg);
     display: block;
     word-wrap: break-word;
     font-weight: 500;
@@ -70,6 +74,7 @@ button {
     border-radius: 4px;
     box-sizing: border-box;
     color: #2a2b2f;
+    font-family: inherit;
     font-size: inherit;
     font-weight: 500;
     text-align: center;
@@ -102,7 +107,7 @@ input[type='text'] {
 }
 
 .content {
-    padding: 20px 15px;
+    padding: 15px;
     border-radius: 4px;
     border: 1px solid lighten(#39404f, 7%);
     color: #fff;