Force correct coloring so that text is always legible on all system themes

Since NUSGet only supports a dark theme right now, but your system may use a light theme, the OS may recolor text on screen to be black on black, which is obviously bad for readability. All text will now be white, so you can always read it.
And hey, maybe there will be a proper light theme soon!

resources/right_arrow.svg

@@ -0,0 +1,59 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   width="16"
+   height="16"
+   viewBox="0 0 16 16"
+   version="1.1"
+   id="svg1"
+   inkscape:version="1.4 (e7c3feb1, 2024-10-09)"
+   sodipodi:docname="right_arrow.svg"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <sodipodi:namedview
+     id="namedview1"
+     pagecolor="#ffffff"
+     bordercolor="#999999"
+     borderopacity="1"
+     inkscape:showpageshadow="2"
+     inkscape:pageopacity="0"
+     inkscape:pagecheckerboard="0"
+     inkscape:deskcolor="#d1d1d1"
+     inkscape:document-units="px"
+     inkscape:zoom="57.72"
+     inkscape:cx="6.8693694"
+     inkscape:cy="7.52772"
+     inkscape:window-width="1512"
+     inkscape:window-height="836"
+     inkscape:window-x="0"
+     inkscape:window-y="38"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="layer1" />
+  <defs
+     id="defs1" />
+  <g
+     inkscape:label="Layer 1"
+     inkscape:groupmode="layer"
+     id="layer1">
+    <path
+       sodipodi:type="star"
+       style="fill:#ffffff;fill-opacity:1;stroke:none;stroke-width:0.154168;stroke-linecap:round;stroke-linejoin:round;stroke-dasharray:none;stroke-opacity:1"
+       id="path1"
+       inkscape:flatsided="false"
+       sodipodi:sides="3"
+       sodipodi:cx="5.0945272"
+       sodipodi:cy="5.9900498"
+       sodipodi:r1="1.9104478"
+       sodipodi:r2="0.95522392"
+       sodipodi:arg1="1.5707963"
+       sodipodi:arg2="2.6179939"
+       inkscape:rounded="0"
+       inkscape:randomized="0"
+       d="M 5.0945273,7.9004977 4.2672791,6.4676618 3.4400309,5.034826 l 1.6544964,-10e-8 1.6544963,0 -0.8272482,1.4328359 z"
+       transform="matrix(0,-2.3912596,1.4291353,0,-0.56059112,19.499764)"
+       inkscape:transform-center-x="-0.68257261" />
+  </g>
+</svg>

resources/style.qss

@@ -145,6 +145,7 @@ QTreeView {
 }
 
 QTreeView QHeaderView::section {
+    color: white;
     background-color: #2b2b2b;
     border: 0;
     font-weight: 500;
@@ -170,7 +171,18 @@ QTreeView QScrollBar:vertical {
     margin-top: 16px;
 }
 
+QTreeView::branch:has-children:!has-siblings:closed,
+QTreeView::branch:closed:has-children:has-siblings {
+        image: url("{IMAGE_PREFIX}/right_arrow.svg");
+}
+
+QTreeView::branch:open:has-children:!has-siblings,
+QTreeView::branch:open:has-children:has-siblings  {
+        image: url("{IMAGE_PREFIX}/down_arrow.svg");
+}
+
 QTextBrowser {
+    color: white;
     background-color: #1a1a1a;
     selection-background-color: #1a73e8;
 }
@@ -326,6 +338,10 @@ QScrollBar::sub-line:horizontal {
     subcontrol-origin: margin;
 }
 
+QMessageBox QLabel {
+    color: white;
+}
+
 WrapCheckboxWidget {
     show-decoration-selected: 1;
     outline: 0;