diff --git a/package-lock.json b/package-lock.json
index 89cf334..39b9512 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -8,6 +8,7 @@
       "name": "scrap-tracer",
       "version": "0.1.0",
       "dependencies": {
+        "@knadh/oat": "0.8.3",
         "@techstark/opencv-js": "4.12.0-release.1"
       },
       "devDependencies": {
@@ -67,6 +68,11 @@
         "@jridgewell/sourcemap-codec": "^1.4.14"
       }
     },
+    "node_modules/@knadh/oat": {
+      "version": "0.8.3",
+      "resolved": "https://registry.npmjs.org/@knadh/oat/-/oat-0.8.3.tgz",
+      "integrity": "sha512-eE07LJ6RpC21PfEbu3U6dFbTO0V6m1OcXocrYr7dwN+Ffr8sx+SqVTPwHO5/+Azv0NWEU8V7frwzBQXdx7CzLA=="
+    },
     "node_modules/@oxc-project/types": {
       "version": "0.154.0",
       "resolved": "https://registry.npmjs.org/@oxc-project/types/-/types-0.154.0.tgz",
diff --git a/package.json b/package.json
index 69a32f2..c59b714 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
     "test": "vitest run"
   },
   "dependencies": {
+    "@knadh/oat": "0.8.3",
     "@techstark/opencv-js": "4.12.0-release.1"
   },
   "devDependencies": {
diff --git a/src/App.svelte b/src/App.svelte
index 18374ff..7696a3d 100644
--- a/src/App.svelte
+++ b/src/App.svelte
@@ -19,6 +19,11 @@
     const file = e.dataTransfer?.files[0];
     if (file) app.loadFile(file);
   }
+
+  function onFile(e: Event & { currentTarget: HTMLInputElement }) {
+    const file = e.currentTarget.files?.[0];
+    if (file) app.loadFile(file);
+  }
 </script>
 
 <div class="layout">
@@ -29,7 +34,11 @@
     {#if app.image}
       <ImageCanvas {app} />
     {:else}
-      <p class="empty">Drop a photo of a scrap piece here, or use “Load photo”.</p>
+      <label class="dropzone">
+        <input type="file" accept="image/*" hidden onchange={onFile} />
+        <strong>Drop a photo of a scrap piece here</strong>
+        <span>or click to choose a file</span>
+      </label>
     {/if}
   </main>
 </div>
@@ -37,8 +46,6 @@
 <style>
   :global(body) {
     margin: 0;
-    font-family: system-ui, sans-serif;
-    color: #222;
   }
   .layout {
     display: grid;
@@ -47,16 +54,33 @@
   }
   aside {
     overflow-y: auto;
-    border-right: 1px solid #ddd;
+    border-right: 1px solid var(--border);
     padding: 16px;
   }
   main {
     position: relative;
     background: #2b2b2b;
   }
-  .empty {
+  .dropzone {
+    position: absolute;
+    inset: 24px;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 4px;
+    border: 2px dashed #555;
+    border-radius: 12px;
     color: #bbb;
-    text-align: center;
-    margin-top: 40vh;
+    cursor: pointer;
+    transition: border-color 0.15s, background-color 0.15s;
+  }
+  .dropzone:hover {
+    border-color: #888;
+    background: rgba(255, 255, 255, 0.03);
+  }
+  .dropzone span {
+    color: #888;
+    font-size: 0.9rem;
   }
 </style>
diff --git a/src/components/Sidebar.svelte b/src/components/Sidebar.svelte
index 14117be..570e3e9 100644
--- a/src/components/Sidebar.svelte
+++ b/src/components/Sidebar.svelte
@@ -6,6 +6,7 @@
   import { scrapFilename, shapeSize } from '../lib/geometry';
 
   let { app }: { app: AppState } = $props();
+  let fileInput: HTMLInputElement;
 
   const size = $derived(app.exportShape ? shapeSize(app.exportShape) : null);
   const nothingDetected = $derived(app.cv !== null && app.image !== null && app.shapePx === null);
@@ -30,24 +31,27 @@
 <h1>Scrap Tracer</h1>
 
 {#if app.cvError}
-  <p class="error">{app.cvError} <button onclick={() => location.reload()}>Reload</button></p>
+  <p class="error">{app.cvError} <button class="outline small" onclick={() => location.reload()}>Reload</button></p>
 {:else if !app.cv}
   <p class="muted">Loading image processing…</p>
 {/if}
 
 <section>
   <h2>1. Photo</h2>
-  <label class="file">Load photo <input type="file" accept="image/*" onchange={onFile} /></label>
+  <button class="outline" onclick={() => fileInput.click()}>{app.image ? 'Replace photo' : 'Load photo'}</button>
+  <input bind:this={fileInput} type="file" accept="image/*" hidden onchange={onFile} />
   {#if app.loadError}<p class="error">{app.loadError}</p>{/if}
 </section>
 
 <section class:disabled={!app.image}>
   <h2>2. Scale</h2>
   <p class="muted">Click both ends of something whose length you know.</p>
-  <button class:active={app.tool === 'scale'} onclick={() => toggle('scale')} disabled={!app.image}>
-    {app.scalePoints.length === 2 ? 'Re-measure' : 'Measure'}
-  </button>
-  <label>Length <input type="number" min="1" step="any" bind:value={app.lengthMm} /> mm</label>
+  <div class="row">
+    <button class:outline={app.tool !== 'scale'} onclick={() => toggle('scale')} disabled={!app.image}>
+      {app.scalePoints.length === 2 ? 'Re-measure' : 'Measure'}
+    </button>
+    <label class="inline">Length <input type="number" min="1" step="any" bind:value={app.lengthMm} /> mm</label>
+  </div>
   {#if app.scaleInvalid}
     <p class="error">Enter a length above 0 and pick two different points.</p>
   {:else if app.pxPerMm}
@@ -58,19 +62,26 @@
 <section class:disabled={!app.image}>
   <h2>3. Outline</h2>
   {#if app.mode === 'auto'}
-    <label>Threshold <input type="range" min="0" max="255" bind:value={app.threshold} /> {app.threshold}</label>
-    <button onclick={() => app.autoThreshold()} disabled={!app.cv || !app.image}>Auto</button>
-    <button class:active={app.tool === 'seed'} onclick={() => toggle('seed')} disabled={!app.image}>Click to pick piece</button>
-  {/if}
-  <button class:active={app.tool === 'draw'} onclick={() => toggle('draw')} disabled={!app.image}>
-    {app.manualOuter.length === 0 ? 'Draw outline manually' : 'Draw a hole'}
-  </button>
-  {#if app.drawing.length > 0}
-    <button onclick={() => app.finishPolygon()}>Finish {app.manualOuter.length === 0 ? 'outline' : 'hole'}</button>
-  {/if}
-  {#if app.mode === 'manual' || app.drawing.length > 0}
-    <button onclick={() => app.clearManual()}>Back to automatic</button>
+    <label>
+      <span class="label-row">Threshold <span class="value">{app.threshold}</span></span>
+      <input type="range" min="0" max="255" bind:value={app.threshold} />
+    </label>
+    <div class="row">
+      <button class="outline" onclick={() => app.autoThreshold()} disabled={!app.cv || !app.image}>Auto</button>
+      <button class:outline={app.tool !== 'seed'} onclick={() => toggle('seed')} disabled={!app.image}>Click to pick piece</button>
+    </div>
   {/if}
+  <div class="row">
+    <button class:outline={app.tool !== 'draw'} onclick={() => toggle('draw')} disabled={!app.image}>
+      {app.manualOuter.length === 0 ? 'Draw outline manually' : 'Draw a hole'}
+    </button>
+    {#if app.drawing.length > 0}
+      <button onclick={() => app.finishPolygon()}>Finish {app.manualOuter.length === 0 ? 'outline' : 'hole'}</button>
+    {/if}
+    {#if app.mode === 'manual' || app.drawing.length > 0}
+      <button class="ghost" onclick={() => app.clearManual()}>Back to automatic</button>
+    {/if}
+  </div>
   {#if nothingDetected}
     <p class="warning">Nothing detected, try adjusting the threshold, clicking the piece, or draw manually.</p>
   {/if}
@@ -79,8 +90,8 @@
 <section class:disabled={!app.pxPerMm}>
   <h2>4. Safety margin</h2>
   <label>
+    <span class="label-row">Margin <span class="value">{app.marginMm} mm</span></span>
     <input type="range" min="-10" max="5" step="0.5" bind:value={app.marginMm} disabled={!app.pxPerMm} />
-    {app.marginMm} mm
   </label>
   {#if !app.pxPerMm}<p class="muted">Set the scale first.</p>{/if}
 </section>
@@ -88,8 +99,10 @@
 <section>
   <h2>5. Export</h2>
   {#if size}<p>Piece: {Math.round(size.width)} × {Math.round(size.height)} mm</p>{/if}
-  <button class="primary" onclick={() => exportAs('dxf')} disabled={!app.exportShape}>Download DXF</button>
-  <button onclick={() => exportAs('svg')} disabled={!app.exportShape}>Download SVG</button>
+  <div class="row">
+    <button onclick={() => exportAs('dxf')} disabled={!app.exportShape}>Download DXF</button>
+    <button class="outline" onclick={() => exportAs('svg')} disabled={!app.exportShape}>Download SVG</button>
+  </div>
   {#if !app.exportShape}
     <p class="muted">{app.pxPerMm ? 'No outline to export yet.' : 'Set the scale first.'}</p>
   {/if}
@@ -97,15 +110,18 @@
 
 <style>
   h1 { font-size: 1.3rem; margin: 0 0 12px; }
-  h2 { font-size: 1rem; margin: 0 0 6px; }
-  section { padding: 12px 0; border-top: 1px solid #eee; display: flex; flex-direction: column; gap: 6px; align-items: flex-start; }
+  h2 { font-size: 1rem; margin: 0; }
+  p { margin: 0; }
+  section { padding: 14px 0; border-top: 1px solid var(--border); display: flex; flex-direction: column; gap: 8px; align-items: flex-start; }
   section.disabled { opacity: 0.5; }
-  label { display: flex; gap: 6px; align-items: center; }
-  input[type='number'] { width: 80px; }
-  .file input { max-width: 200px; }
-  button.active { outline: 2px solid #2962ff; }
-  button.primary { font-weight: bold; }
-  .muted { color: #777; margin: 0; font-size: 0.9rem; }
-  .error { color: #c62828; margin: 0; }
-  .warning { color: #e65100; margin: 0; }
+  section > label { align-self: stretch; }
+  input[type='range'] { width: 100%; }
+  .row { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }
+  .inline { display: flex; gap: 6px; align-items: center; }
+  .inline input { width: 90px; margin: 0; }
+  .label-row { display: flex; justify-content: space-between; }
+  .value { color: var(--muted-foreground); font-variant-numeric: tabular-nums; }
+  .muted { color: var(--muted-foreground); font-size: 0.875rem; }
+  .error { color: var(--danger); }
+  .warning { color: var(--warning); }
 </style>
diff --git a/src/main.ts b/src/main.ts
index 3fcb539..c9db2ce 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,3 +1,4 @@
+import '@knadh/oat/oat.min.css';
 import { mount } from 'svelte';
 import App from './App.svelte';