Added option to invert thumbnails in dark mode

src-ui/src/app/components/document-list/document-card-small/document-card-small.component.html

@@ -1,7 +1,7 @@
 <div class="col p-2 h-100">
   <div class="card h-100 shadow-sm document-card" [class.card-selected]="selected">
     <div class="border-bottom doc-img-container" [class.doc-img-background-selected]="selected" (click)="this.toggleSelected.emit($event)">
-      <img class="card-img doc-img rounded-top" [src]="getThumbUrl()">
+      <img class="card-img {{ getIsThumbInverted() ? 'doc-img-inverted' : 'doc-img' }} rounded-top" [src]="getThumbUrl()">
 
       <div class="border-right border-bottom bg-light p-1 rounded document-card-check">
         <div class="custom-control custom-checkbox">

src-ui/src/app/components/document-list/document-card-small/document-card-small.component.scss

@@ -1,6 +1,6 @@
 @import "/src/theme";
 
-.doc-img {
+.doc-img, .doc-img-inverted {
   object-fit: cover;
   object-position: top left;
   height: 200px;

src-ui/src/app/components/document-list/document-card-small/document-card-small.component.ts

@@ -2,6 +2,7 @@ import { Component, EventEmitter, Input, OnInit, Output } from '@angular/core';
 import { map } from 'rxjs/operators';
 import { PaperlessDocument } from 'src/app/data/paperless-document';
 import { DocumentService } from 'src/app/services/rest/document.service';
+import { SettingsService, SETTINGS_KEYS } from 'src/app/services/settings.service';
 
 @Component({
   selector: 'app-document-card-small',
@@ -10,7 +11,7 @@ import { DocumentService } from 'src/app/services/rest/document.service';
 })
 export class DocumentCardSmallComponent implements OnInit {
 
-  constructor(private documentService: DocumentService) { }
+  constructor(private documentService: DocumentService, private settingsService: SettingsService) { }
 
   @Input()
   selected = false
@@ -32,6 +33,10 @@ export class DocumentCardSmallComponent implements OnInit {
   ngOnInit(): void {
   }
 
+  getIsThumbInverted() {
+    return this.settingsService.get(SETTINGS_KEYS.DARK_MODE_THUMB_INVERTED)
+  }
+
   getThumbUrl() {
     return this.documentService.getThumbUrl(this.document.id)
   }