fix: prevent FAB button overflow on very small screens (iPhone 13 mini)

- Add media query for screens ≤400px (iPhone 13 mini = 375px)
- Reduce button size to 34px and icon size to 16px
- Recalculate 6-button positions with 6px gaps (234px total width)
- Ensures buttons stay centered within narrow viewports

static/css/04-interactive/_scroll-behavior.css

@@ -379,6 +379,95 @@
     }
 }
 
+/* ========================================
+   Very Small Screens: iPhone 13 mini (375px) and smaller
+   Tighter button spacing to prevent overflow
+   ======================================== */
+@media (max-width: 400px) {
+    /* Smaller buttons for very small screens */
+    .download-btn,
+    .print-friendly-btn,
+    .fixed-btn.contact-btn,
+    .shortcuts-btn,
+    .info-button,
+    .back-to-top,
+    .color-theme-switcher {
+        width: 34px !important;
+        height: 34px !important;
+    }
+
+    /* Smaller icons */
+    .download-btn iconify-icon,
+    .print-friendly-btn iconify-icon,
+    .fixed-btn.contact-btn iconify-icon,
+    .shortcuts-btn iconify-icon,
+    .info-button iconify-icon,
+    .back-to-top iconify-icon,
+    .color-theme-switcher iconify-icon {
+        width: 16px !important;
+        height: 16px !important;
+        font-size: 16px !important;
+        max-width: 16px !important;
+    }
+
+    /* REAL MOBILE DEVICES: 6 buttons tightly spaced */
+    /* 6 buttons * 34px + 5 gaps * 6px = 234px total, center offset = -117px */
+    .is-mobile-device .download-btn {
+        left: calc(50% - 117px) !important;
+    }
+
+    .is-mobile-device .print-friendly-btn {
+        left: calc(50% - 77px) !important;
+    }
+
+    .is-mobile-device .fixed-btn.contact-btn {
+        left: calc(50% - 37px) !important;
+    }
+
+    /* Theme switcher - fourth position: +3px from center */
+    .is-mobile-device .color-theme-switcher {
+        left: calc(50% + 3px) !important;
+    }
+
+    .is-mobile-device .info-button {
+        left: calc(50% + 43px) !important;
+    }
+
+    .is-mobile-device .back-to-top {
+        left: calc(50% + 83px) !important;
+    }
+
+    /* Non-mobile (desktop in mobile emulation): 7 buttons */
+    /* 7 buttons * 34px + 6 gaps * 6px = 274px total, center offset = -137px */
+    .download-btn {
+        left: calc(50% - 137px) !important;
+    }
+
+    .print-friendly-btn {
+        left: calc(50% - 97px) !important;
+    }
+
+    .fixed-btn.contact-btn {
+        left: calc(50% - 57px) !important;
+    }
+
+    .shortcuts-btn {
+        left: calc(50% - 17px) !important;
+    }
+
+    .color-theme-switcher {
+        left: calc(50% + 23px) !important;
+    }
+
+    .info-button {
+        left: calc(50% + 63px) !important;
+    }
+
+    .back-to-top {
+        left: calc(50% + 103px) !important;
+    }
+}
+
 /* ========================================
    Mobile: Keep action bar visible (prevent hiding on scroll)
    ======================================== */