diff --git a/website/static/website/css/publications.css b/website/static/website/css/publications.css
index a65b651c..4483421c 100644
--- a/website/static/website/css/publications.css
+++ b/website/static/website/css/publications.css
@@ -694,9 +694,14 @@
    and style its contents. */
 
 .artifact-preview-popover {
-  /* Compact card. Talk slides are landscape, so width drives the size; keep it
-     modest. Posters (often portrait) are bounded by the image max-height. */
-  max-width: 272px;
+  /* The card hugs its image: thumbnailPreview.js sizes the image to a fixed box
+     and the card shrink-wraps it. base.css sets a global `.popover { width: 50vw;
+     min-width: 300px }`, so we must reset both here or the card can't shrink to
+     the image (that was the whitespace beside portrait posters). max-width is a
+     generous ceiling so a full-width landscape image (+ padding) is never clipped. */
+  width: auto;
+  min-width: 0;
+  max-width: 300px;
   /* Bootstrap sets .popover { display: none }; the JS reveals it. Keep it
      above page chrome but below modals. */
   z-index: 1060;
@@ -713,12 +718,16 @@
 
 .artifact-preview-image {
   display: block;
-  width: 100%;
-  height: auto;
-  /* Never let a tall poster run past the viewport. */
-  max-height: 45vh;
-  object-fit: contain;
-  border-radius: var(--border-radius-sm, 3px);
+  /* Height-capped (not width-driven), so portrait posters stay compact instead
+     of running tall; landscape ones still fill the card width. width/height are
+     left to intrinsic aspect, bounded by the maxes. Narrower (portrait) images
+     are centered. */
+  margin: 0 auto;
+  max-width: 100%;
+  max-height: 240px;
+  /* Rounded rect + subtle outline so the thumbnail reads as a framed preview. */
+  border-radius: var(--border-radius-md, 8px);
+  border: 1px solid var(--color-border, #d0d0d0);
 }
 
 .artifact-preview-actions {
@@ -750,9 +759,10 @@
   outline-offset: var(--focus-ring-offset, 2px);
 }
 
-/* File size, pushed to the trailing edge of each action row. */
+/* File size sits right after its label (not pushed to the trailing edge), so a
+   lone action doesn't leave an awkward gap when the card is as wide as the
+   poster image. */
 .artifact-preview-size {
-  margin-left: auto;
   color: var(--color-text-secondary, #666);
   font-size: 0.85em;
 }
diff --git a/website/static/website/js/thumbnailPreview.js b/website/static/website/js/thumbnailPreview.js
index 0352e047..0210c112 100644
--- a/website/static/website/js/thumbnailPreview.js
+++ b/website/static/website/js/thumbnailPreview.js
@@ -59,6 +59,12 @@
   const ARROW_HALF = 11;
   /** Delay (ms) before a hover-opened card hides, so the pointer can reach it. */
   const HIDE_DELAY = 140;
+  /** Box the preview image is fit into (px). The image is sized explicitly in
+   *  JS to these bounds so the card hugs it — CSS shrink-to-fit uses the image's
+   *  intrinsic (600px-wide thumbnail) size and can't account for the height cap,
+   *  which is what left whitespace beside portrait thumbnails. */
+  const PREVIEW_MAX_W = 260;
+  const PREVIEW_MAX_H = 240;
 
   /* ===========================================================================
      STATE
@@ -126,6 +132,35 @@
     content.appendChild(template.content.cloneNode(true));
     popover.appendChild(content);
 
+    // Size the preview image explicitly (fit within PREVIEW_MAX_W x
+    // PREVIEW_MAX_H, preserving aspect) so the card hugs it. Without a definite
+    // width the card sizes to the thumbnail's intrinsic 600px (capped), then the
+    // height cap shrinks the image — leaving whitespace beside portrait posters.
+    const img = popover.querySelector('.artifact-preview-image');
+    if (img) {
+      const sizeToImage = function () {
+        const nw = img.naturalWidth;
+        const nh = img.naturalHeight;
+        if (!nw || !nh) {
+          return;
+        }
+        const scale = Math.min(PREVIEW_MAX_W / nw, PREVIEW_MAX_H / nh, 1);
+        img.style.width = Math.round(nw * scale) + 'px';
+        img.style.height = Math.round(nh * scale) + 'px';
+        // The card's size just changed; re-anchor it to the trigger.
+        if (activePopover === popover && activeTrigger === trigger) {
+          positionPopover(trigger, popover);
+        }
+      };
+      // Cached images are already complete (no 'load' will fire); size now so the
+      // popover is measured correctly when open() positions it.
+      if (img.complete && img.naturalWidth) {
+        sizeToImage();
+      } else {
+        img.addEventListener('load', sizeToImage);
+      }
+    }
+
     return popover;
   }