UI: Made canvas borders visible for both light and dark themes

pages/paint.html

@@ -1,7 +1,7 @@
 {{ define "paint" }}
 
-<canvas class="row border border-dark" id="drawingCanvas" width="256" height="256"></canvas>
-<input class="row border border-dark" type="color" id="colorPicker" value="#000000" aria-label="Drawing color">
+<canvas class="row border border-secondary" id="drawingCanvas" width="256" height="256"></canvas>
+<input class="row border border-secondary" type="color" id="colorPicker" value="#000000" aria-label="Drawing color">
 
 <script>
     const canvas = document.getElementById('drawingCanvas');