"Mr. Okafor Explains" 是一张数学辅导频道的 YouTube 横幅，采用黑板风格。干净的粉笔字和「一步步讲代数与几何」的标语位于绿色黑板正中，手绘的公式、三角形和圆都放在边缘。可以换成你自己的名字和科目。

Create a finished 16:9 YouTube channel banner at 2848 × 1600 px. Use a continuous deep green chalkboard background edge to edge, with subtle slate-green board grain and faint erased-chalk smudges. Keep all essential content inside the central YouTube safe band: approximately the middle 60% of the width and 29% of the height. Center the channel name as the dominant element, in the upper half of that band: render the exact text “Mr. Okafor Explains” in large, bold, hand-drawn chalk lettering, optically crisp and readable at small avatar and phone-thumbnail scale. Use broad, slightly irregular white chalk strokes, open counters, rounded hand-worked terminals, and lightly dusty edges; no ornate flourishes. Directly beneath it, set the exact tagline “Algebra and geometry, step by step” in smaller but clearly legible white chalk lettering, centered with generous separation. Preserve the spelling, capitalization, and punctuation exactly; add no other words, labels, logos, icons, or social details. At the far left and right edges, add a few restrained hand-drawn chalk marks: partial algebraic symbols, a simple triangle construction, a circle with a radius, and a small angle diagram. Keep these as secondary decorative fragments outside the safe band, cropped or incomplete so they do not become additional readable copy. Leave the central field behind the lettering uncluttered. Balanced, centered composition, strong size contrast, matte chalkboard surface, chalk dust visible only close to the marks, soft even overhead illumination, high legibility, clean graphic finish. No border, frame, drop shadow, faces, or photographic props.