Inputs, selects, and textareas accept normal CSS for padding, border, radius, and background. Style focus (:focus/:focus-visible) for clarity, and use validation pseudo-classes :valid, :invalid, :required for live feedback. Some control internals stay browser-controlled, but the basics are yours.
<!doctype html><html><head><meta charset="utf-8">
<style>input{padding:8px 10px;background:#0c081a;color:#e6e0ff;border:1px solid #2a1d4a;border-radius:4px}input:focus{outline:2px solid #b388ff}input:invalid{border-color:#ff7a8a}</style></head><body style="background:#06040d;padding:20px"><input type="email" required placeholder="email"></body></html>