Add custom spoiler component

src/renderer/components/spoiler/spoiler.module.scss

@@ -1,9 +1,31 @@
-.control {
-    color: var(--btn-subtle-fg);
-    font-weight: 600;
-}
-
 .control:hover {
     color: var(--btn-subtle-fg-hover);
     text-decoration: none;
 }
+
+.spoiler {
+    position: relative;
+    text-align: justify;
+    width: 100%;
+    height: 100%;
+    overflow: hidden;
+}
+
+.spoiler:not(.is-expanded).can-expand:after {
+    position: absolute;
+    left: 0;
+    bottom: 0;
+    width: 100%;
+    height: 100%;
+    content: '';
+    background: linear-gradient(to top, var(--main-bg) 10%, transparent 60%);
+    pointer-events: none;
+}
+
+.spoiler.can-expand {
+    cursor: pointer;
+}
+
+.spoiler.is-expanded {
+    max-height: 2500px !important;
+}