GradientForge copies a complete background-image declaration, not a class or a stylesheet. Put that declaration inside an existing CSS rule. A gradient is an image value, so placing linear-gradient() in background-color is not equivalent.
Read the property, function and stop list
background-image: linear-gradient(135deg, #5B21B6 0%, #22D3EE 100%); contains a property name, colon, image function and final semicolon. Inside the parentheses, 135deg is the direction; commas separate the colour stops. Each stop has a six-digit hex colour and a percentage. Radial output replaces the direction with ellipse at 50% 50%; conic output uses from 135deg at 50% 50%. Do not copy a radial prefix into a linear function.
Keep the surrounding CSS explicit
Set a separate background-color as a fallback. The copied declaration does not set dimensions, padding, text colour or contrast. A later background shorthand can reset background-image, so inspect the final cascade if the gradient disappears. This generator emits one non-repeating gradient with integer percentages and opaque hex colours; it does not parse existing CSS, create multiple background layers or supply vendor prefixes.
Verify the declaration in its real context
Keep a background-color fallback and save the CSS before reloading: palettes are not stored. Test the target browsers and sizes. Check text contrast across the visible gradient, not just one point; the preview certifies neither accessibility nor compatibility.