Refactor Dockerfile and enhance CSS for improved theme support

- Updated Dockerfile to standardize environment variable syntax and improve readability.
- Added new CSS variables for chart grid color and enhanced dark theme contrast for CPU chart statistics.
- Modified index.html to utilize new CSS variables for better theme adaptability and improved chart rendering.

static/css/main.css

@@ -38,6 +38,7 @@
   --border: 1px;
   --depth: 1;
   --noise: 0;
+  --chart-grid-color: color-mix(in oklch, var(--color-base-content) 22%, transparent);
 }
 
 @plugin "daisyui/theme" {
@@ -74,6 +75,7 @@
   --border: 1px;
   --depth: 1;
   --noise: 0;
+  --chart-grid-color: color-mix(in oklch, var(--color-base-content) 22%, transparent);
 }
 
 /* VTB gradient (both themes) */
@@ -142,6 +144,14 @@
   background-color: color-mix(in oklch, var(--color-base-content) 12%, transparent);
 }
 
+/* Dark theme: better contrast for CPU chart stats (Mean, ±0.5σ) */
+[data-theme=dark] section[aria-label="CPU distribution chart"] .text-success {
+  color: oklch(85% 0.16 163);
+}
+[data-theme=dark] section[aria-label="CPU distribution chart"] .text-error\/60 {
+  color: oklch(82% 0.18 13);
+}
+
 /* Accessibility: ensure focus ring is visible on key controls */
 .btn:focus-visible,
 .select:focus-within,