Area Between Curves

import matplotlib.pyplot as plt
import numpy as np

# === STYLE CONFIG ===
COLORS = {
    'upper': '#8B5CF6',      # Violet
    'lower': '#06B6D4',      # Cyan
    'fill': '#8B5CF6',       # Violet (alpha)
    'background': '#FAFBFC',
    'text_muted': '#64748B',
    'grid': '#E2E8F0',
}

# === DATA ===
x = np.linspace(0, 10, 100)
y_upper = 6 + 2 * np.sin(x) + 0.5 * np.cos(2 * x)
y_lower = 3 + 1.5 * np.sin(x) - 0.3 * np.cos(2 * x)

# === FIGURE ===
fig, ax = plt.subplots(figsize=(10, 6), dpi=100)
ax.set_facecolor(COLORS['background'])
fig.patch.set_facecolor(COLORS['background'])

# === PLOT ===
ax.fill_between(x, y_lower, y_upper, color=COLORS['fill'], alpha=0.2, label='Range')
ax.plot(x, y_upper, color=COLORS['upper'], linewidth=2.5, label='Upper bound')
ax.plot(x, y_lower, color=COLORS['lower'], linewidth=2.5, label='Lower bound')

# === AXES ===
ax.set_xlim(0, 10)
ax.set_ylim(0, 10)
ax.set_xlabel('X', fontsize=10, color=COLORS['text_muted'], labelpad=10)
ax.set_ylabel('Y', fontsize=10, color=COLORS['text_muted'], labelpad=10)

# === STYLING ===
for spine in ['top', 'right']:
    ax.spines[spine].set_visible(False)
for spine in ['bottom', 'left']:
    ax.spines[spine].set_color(COLORS['grid'])

ax.yaxis.grid(True, color=COLORS['grid'], linewidth=0.5, alpha=0.7)
ax.xaxis.grid(False)
ax.set_axisbelow(True)
ax.tick_params(axis='both', colors=COLORS['text_muted'], labelsize=9, length=0, pad=8)

ax.legend(loc='upper center', bbox_to_anchor=(0.5, -0.12),
          ncol=3, frameon=False, fontsize=9, labelcolor=COLORS['text_muted'])

plt.tight_layout()
plt.show()