Modal dialog — overlay + centered box

A dialog that floats above the page. Dark overlay behind, centered white box, close button.

style.css v3.1

style.css — the CSS rules

/* The overlay — covers the whole page */
.modal-overlay {
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  background: rgba(0,0,0,0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
  backdrop-filter: blur(2px);
}

/* The modal box itself */
.modal {
  background: white;
  border-radius: 12px;
  padding: 0;
  width: 90%;
  max-width: 500px;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
  animation: modalIn 0.2s ease-out;
}

@keyframes modalIn {
  from { transform: scale(0.9); opacity: 0; }
  to   { transform: scale(1);   opacity: 1; }
}

.modal .modal-header {
  padding: 1.2rem 1.5rem;
  border-bottom: 1px solid #eee;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.modal .modal-header h3 {
  margin: 0;
  font-size: 1.1rem;
}

.modal .close-btn {
  background: none;
  border: none;
  font-size: 1.5rem;
  color: #999;
  cursor: pointer;
  padding: 0;
  line-height: 1;
}

.modal .close-btn:hover { color: #333; }

.modal .modal-body {
  padding: 1.5rem;
  color: #333;
  line-height: 1.6;
}

.modal .modal-footer {
  padding: 1rem 1.5rem;
  border-top: 1px solid #eee;
  display: flex;
  gap: 0.5rem;
  justify-content: flex-end;
}

.modal .btn-secondary {
  background: #f5f5f5;
  border: 1px solid #ddd;
  border-radius: 6px;
  padding: 0.5rem 1.2rem;
  cursor: pointer;
}

.modal .btn-primary {
  background: #a0c000;
  color: white;
  border: none;
  border-radius: 6px;
  padding: 0.5rem 1.2rem;
  cursor: pointer;
}

index.html — the HTML structure (what the CSS targets)

<div class="modal-overlay">
  <div class="modal">
    <div class="modal-header">
      <h3>Delete Model?</h3>
      <button class="close-btn">&times;</button>
    </div>
    <div class="modal-body">
      Are you sure you want to delete <strong>RandomForest_v2</strong>?
      This action cannot be undone. All benchmark results for this model
      will also be removed.
    </div>
    <div class="modal-footer">
      <button class="btn-secondary">Cancel</button>
      <button class="btn-primary">Delete</button>
    </div>
  </div>
</div>

Live preview updates as you type

🧠 How it works

position: fixed + top: 0; width: 100%; height: 100% — the overlay covers the ENTIRE viewport. background: rgba(0,0,0,0.5) — semi-transparent black. Dims the page behind the modal. display: flex + align-items: center + justify-content: center — centers the modal box. z-index: 1000 — modal is above everything else on the page. backdrop-filter: blur(2px) — blurs the content behind the overlay (modern, supported in most browsers). max-width: 500px + width: 90% — responsive: 500px on desktop, 90% on mobile. @keyframes modalIn — the modal scales up from 0.9 to 1.0 with a fade-in. Feels smooth. Structure: header (title + close), body (content), footer (action buttons). Classic dialog pattern.

✏️ Try these changes

Change rgba(0,0,0,0.5) to rgba(0,0,0,0.8)
→ darker overlay — more dramatic
Change max-width: 500px to 800px
→ wider modal
Change the animation duration from 0.2s to 0.5s
→ slower entrance
Remove backdrop-filter: blur(2px)
→ no blur behind the modal
Change border-radius: 12px to 0
→ sharp corners — more 'system dialog' look

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