Implement WebGL page reserve navigation

public/css/style.css

@@ -2068,6 +2068,71 @@ body.webgl-mode .choice-list kbd {
     opacity: 0.38;
 }
 
+#webgl_book_navigation {
+    position: fixed;
+    z-index: 52;
+    left: 50%;
+    bottom: 18px;
+    transform: translateX(-50%);
+    width: min(820px, calc(100vw - 32px));
+    display: grid;
+    grid-template-columns: 34px 34px minmax(180px, 1fr) 34px 34px;
+    align-items: center;
+    gap: 10px;
+    padding: 10px 12px;
+    box-sizing: border-box;
+    color: rgba(246, 231, 201, 0.94);
+    background: rgba(12, 9, 7, 0.62);
+    border: 1px solid rgba(246, 231, 201, 0.24);
+    border-radius: 6px;
+    backdrop-filter: blur(10px);
+}
+
+.webgl-book-nav-button {
+    width: 34px;
+    height: 30px;
+    display: grid;
+    place-items: center;
+    color: rgba(246, 231, 201, 0.94);
+    background: rgba(44, 28, 17, 0.74);
+    border: 1px solid rgba(246, 231, 201, 0.26);
+    border-radius: 4px;
+    cursor: pointer;
+}
+
+.webgl-book-nav-button:disabled {
+    opacity: 0.36;
+    cursor: var(--default-cursor, default);
+}
+
+.webgl-book-nav-slider-wrap {
+    display: grid;
+    grid-template-columns: minmax(0, 1fr) minmax(72px, auto);
+    align-items: center;
+    gap: 10px;
+    min-width: 0;
+}
+
+#webgl_book_nav_position {
+    width: 100%;
+    accent-color: #f0cd8e;
+    background:
+        linear-gradient(90deg,
+            rgba(240, 205, 142, 0.48) 0%,
+            rgba(240, 205, 142, 0.48) calc(var(--book-nav-written, 0) * 100%),
+            rgba(246, 231, 201, 0.18) calc(var(--book-nav-written, 0) * 100%),
+            rgba(246, 231, 201, 0.18) calc(var(--book-nav-reserve-start, 1) * 100%),
+            rgba(80, 40, 34, 0.58) calc(var(--book-nav-reserve-start, 1) * 100%),
+            rgba(80, 40, 34, 0.58) 100%);
+}
+
+.webgl-book-nav-page-label {
+    min-width: 72px;
+    text-align: right;
+    font-size: 13px;
+    line-height: 1;
+}
+
 #modal_overview {
     position: fixed;
     z-index: 45;