refactor(cc-dark-theme): organize styles in several files

Until now we had a single file for the dark theme styles with ~2500
lines, with several sections which were marked with CSS comments.

This CL separates this file into several ones to improve its
maintainability, using the folder structure suggested by
https://sass-guidelin.es/#architecture.

Fixed: twpowertools:21
Change-Id: I0c1741f58b470085c0a499b32aa64feb43d8ad31
diff --git a/src/ccDarkTheme/components/buttons/_button.scss b/src/ccDarkTheme/components/buttons/_button.scss
new file mode 100644
index 0000000..10ad660
--- /dev/null
+++ b/src/ccDarkTheme/components/buttons/_button.scss
@@ -0,0 +1,7 @@
+material-button[disabled] {
+  color: rgba(255, 255, 255, .26)!important;
+}
+
+.mdc-button {
+  --gm-colortextbutton-disabled-ink-color: rgba(255, 255, 255, .26);
+}
diff --git a/src/ccDarkTheme/components/buttons/_index.scss b/src/ccDarkTheme/components/buttons/_index.scss
new file mode 100644
index 0000000..ab002dc
--- /dev/null
+++ b/src/ccDarkTheme/components/buttons/_index.scss
@@ -0,0 +1,4 @@
+@forward 'button';
+@forward 'yes-no';
+@forward 'reply';
+@forward 'skip-to-main';
diff --git a/src/ccDarkTheme/components/buttons/_reply.scss b/src/ccDarkTheme/components/buttons/_reply.scss
new file mode 100644
index 0000000..bc7aeaf
--- /dev/null
+++ b/src/ccDarkTheme/components/buttons/_reply.scss
@@ -0,0 +1,5 @@
+material-fab.reply-button,
+    material-fab.reply-fab {
+  background-color: var(--TWPT-link)!important;
+  color: var(--TWPT-primary-background)!important;
+}
diff --git a/src/ccDarkTheme/components/buttons/_skip-to-main.scss b/src/ccDarkTheme/components/buttons/_skip-to-main.scss
new file mode 100644
index 0000000..17eb10f
--- /dev/null
+++ b/src/ccDarkTheme/components/buttons/_skip-to-main.scss
@@ -0,0 +1,3 @@
+.skip-to-main:focus {
+  background: revert!important;
+}
diff --git a/src/ccDarkTheme/components/buttons/_yes-no.scss b/src/ccDarkTheme/components/buttons/_yes-no.scss
new file mode 100644
index 0000000..3127b9e
--- /dev/null
+++ b/src/ccDarkTheme/components/buttons/_yes-no.scss
@@ -0,0 +1,21 @@
+material-yes-no-buttons material-button:not([disabled]).highlighted:not([raised]) {
+  color: var(--TWPT-blue-A100)!important;
+}
+
+material-yes-no-buttons material-button:not([disabled]).highlighted:not([raised]):is(:hover, :focus) {
+  background-color: revert!important;
+}
+
+material-yes-no-buttons material-button:not([disabled]).highlighted:not([raised]):is(:hover, :focus):after {
+  content: "";
+  display: block;
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background-color: currentColor;
+  opacity: .12;
+  border-radius: inherit;
+  pointer-events: none;
+}